X-ray tube and method and apparatus for analyzing fluid streams using x-rays

ABSTRACT

A method and apparatus for analyzing fluids by means of x-ray fluorescence. The method and apparatus are applicable to any fluid, including liquids and gases, having at least one component that emits x-ray fluorescence when exposed to x-rays. The apparatus includes an x-ray source ( 82 ) including an x-ray tube ( 64 ) having improved heat dissipating properties due to the thermal coupling of the x-ray tube with a thermally-conductive, dielectric material ( 70, 1150 ). The x-ray tube also includes means for aligning ( 100, 2150, 2715 ) the x-ray tube with the x-ray source housing whereby the orientation of the x-ray beam produced by the x-ray source can be optimized, and stabilized various over operating conditions. The method and apparatus may also include an x-ray detector having a small-area, for example, a PIN-diode type semiconductor x-ray detector ( 120 ), that can provide effective x-ray detection at room temperature. One aspect of the disclosed invention is most amenable to the analysis of sulfur in petroleum-based fuels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT Application PCT/US02/38792,filed Dec. 4, 2002, and published under PCT Article 21(2) in English asWO 03/048745 A2 on Jun. 12, 2003. PCT/US02/38792 claimed the priority ofthe United States applications identified below, which are assigned tothe same assignee as this application. The entire disclosures ofPCT/US02/38792 and the below-listed applications are hereby incorporatedherein by reference in their entirety:

-   -   “X-RAY TUBE AND METHOD AND APPARATUS FOR ANALYZING FLUID STREAMS        USING X-RAYS” by Radley, et al. U.S. Ser. No. 60/336,584 filed        Dec. 4, 2001 (attorney docket 0444.045P);    -   “A METHOD AND APPARATUS FOR DIRECTING X-RAYS” by Radley, U.S.        Ser. No. 60/383,990 filed May 29, 2002 (attorney docket        0444.055P);    -   “X-RAY SOURCE ASSEMBLY HAVING ENHANCED OUTPUT STABILITY” by        Radley, et al., U.S. Ser. No. 60/398,965 filed Jul. 26, 2002        (attorney docket 0444.056P);    -   “METHOD AND DEVICE FOR COOLING AND ELECTRICALLY INSULATING A        HIGH-VOLTAGE, HEAT-GENERATING COMPONENT” by Radley, U.S. Ser.        No. 60/398,968 filed Jul. 26, 2002 (attorney docket 0444.057P);    -   “AN ELECTRICAL CONNECTOR, A CABLE SLEEVE, AND A METHOD FOR        FABRICATING AN ELECTRICAL CONNECTION” by Radley, U.S. Ser. No.        10/206,531 filed Jul. 26, 2002 (attorney docket 0444.058); and    -   “DIAGNOSING SYSTEM FOR AN X-RAY SOURCE ASSEMBLY” by Radley, et        al., U.S. Ser. No. 60/398,966 filed Jul. 26, 2002 (attorney        docket 0444.065P).

TECHNICAL FIELD

This invention relates generally to apparatus and methods used for x-rayfluorescence analysis, for example, x-ray fluorescence analysis of fluidstreams. Specifically, the present invention provides improved methodsand apparatus for detecting the presence of sulfur in fluid fuelstreams; with improved methods and apparatus for removing heat fromhigh-power, high-voltage electrical components, and including enhancedstability over a range of operating conditions.

BACKGROUND OF THE INVENTION

The implementation of x-ray analysis methods has been one of the mostsignificant developments in twentieth-century science and technology.The use of x-ray diffraction, x-ray spectroscopy, x-ray imaging, andother x-ray analysis techniques has led to a profound increase inknowledge in virtually all scientific fields.

X-ray fluorescence (XRF) is an analytical technique by which a substanceis exposed to a beam of x-rays to determine, for example, the presenceof certain chemicals. In the XRF technique, at least some of thechemical constituents of the substance exposed to x-rays can absorbx-ray photons and produce characteristic secondary fluorescence x-rays.These secondary x-rays are characteristic of the chemical constituentsin the substance. Upon appropriate detection and analysis thesesecondary x-rays can be used to characterize one or more of the chemicalconstituents of the substance. The XRF technique has broad applicationsin many chemical and material science fields, including medicalanalysis, semiconductor chip evaluation, and forensics, among others.

XRF methods have often been used for measuring the sulfur content offuels, for example, petroleum-based fuels, such as gasoline and dieselfuels. Existing XRF systems have been known to detect sulfur in fuelsdown to as low as 5 parts per million (ppm) by weight; however, thisdetectability has required stringent control conditions, for example,this detectability is typically achievable only in the laboratory. Underless rigorous conditions, for example, in the field, existing XRFmethods, such as ASTM standard method D2622, are limited to detectingsulfur concentrations in fuels only down to about 30 ppm. Among otherthings, the present invention provides improvements in repeatability anddetectability of XRF detection of sulfur in fuels.

In these and many other industries, for example, the analyticalindustry, x-ray beam generating devices are commonly used. X-ray beamgenerating devices may typically include x-ray tubes which generatex-rays by impinging electron beams onto metal surfaces. X-ray tubestypically include an electron gun which generates an electron beam andan anode which provides the metal surface upon which the electron beamis directed. Typically, the electron gun and anode are operated in threedifferent modes: 1) with a grounded anode and the electron gun operatedat high positive voltage; 2) with a grounded electron gun (that is, agrounded cathode) and the anode operated at high negative voltage; or 3)in a “bi-polar” mode with cathode and anode operated at differentvoltages. For low power applications, the x-ray tube is typicallyoperated with a “grounded cathode” wherein the electron gun and itsadjacent components are operated at essentially ground potential and theanode and its adjacent components, if any, at high electric potential,for example, at 50 kilovolts (kv) or higher.

The impingement of the electron beam on the anode and the operation ofthe anode at such high voltages generates heat, typically a lot of heat,for example, at least about 50 Watts. In order to dissipate this heat,an x-ray tube is typically immersed in a cooling fluid, that is, athermally-conductive cooling fluid, such as a cooling oil having a highenough dielectric strength to prevent the cooling oil from breaking downand permitting arcing at high potential. A typical high-dielectriccooling fluid is Diala Ax oil provided by Shell Oil Company.

In the conventional art, the x-ray tube and the cooling oil aretypically held inside a sealed container, for example, a cylindricalmetal container, wherein the x-ray tube is immersed in oil andelectrically isolated from the container. The resulting structureincludes an x-ray tube having a high-temperature anode at high potentialsurrounded by a high dielectric strength oil, all encased inside asealed metal container. As a result, the oil typically convects insidethe container as it is heated by the anode. This heating of the oilthrough convection also heats the walls of the container and the x-raytube itself via convection. Conventionally, the outside walls of thesealed container may be cooled directly by, for example, naturalconvection, forced air convection, or flowing a cooling fluid over theoutside of the container. This chain of convective and conductive heattransfer is an inefficient cooling process. Even for a conventionalx-ray tube requiring modest power dissipation, the x-ray beam device andits components typically reach high temperatures, for example, as muchas 120 degrees C. Such high temperatures are undesirable and can bedetrimental to the operation of the x-ray tube.

Thus, there is a need in the art to provide simplified methods forcooling an x-ray beam device, or any other high-temperature, highvoltage devices.

Moreover, the ability to focus x-ray radiation, until recentlyunachievable, has enabled reductions in the size and cost of x-raysources, and hence x-ray systems, that find use in a variety ofapplications. U.S. Pat. No. 6,351,520 describes one example of an x-raysource which includes a focusing element that enables the production ofa high intensity, small diameter x-ray spot size while incorporating alow-power, reduced-cost x-ray source.

While progress in the ability to focus x-ray radiation has recently beenachieved, there remains a need for further enhancements to x-ray sourceassemblies, for example, to improve output stability of an x-ray beamunder a variety of operating conditions. The present invention isdirected to meeting this need.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus which address manyof the limitations of prior art methods and apparatus. In the followingdescription, and throughout this specification, the expressions “focus”,“focusing”, and “focused”, among others, repeatedly appear, for example,as in “focusing device”, “x-ray focusing device”, “means for focusing”,“focusing optic”, among others. Though according to the presentinvention these expressions can apply to devices or methods in whichx-rays are indeed “focused”, for example, caused to be concentrated,these expressions are not meant to limit the invention to devices that“focus” x-rays. According to the present invention, the term “focus” andrelated terms are intended to also serve to identify methods and deviceswhich collect x-rays, collimate x-rays, converge x-rays, diverge x-rays,or devices that in any way vary the intensity, direction, path, or shapeof x-rays. All these means of handling, manipulating, varying,modifying, or treating x-rays are encompassed in this specification bythe term “focus” and its related terms.

One aspect of the present invention is an x-ray tube assemblycomprising: an x-ray tube; and a thermally-conductive, dielectricmaterial thermally coupled to the x-ray tube for removing heat generatedby the x-ray tube. The thermally-conductive, dielectric material may bealuminum nitride, beryllium oxide, and diamond-like carbon, amongothers. The x-ray tube assembly may include an x-ray tube having a firstend and a second end, and the first end of the x-ray tube including anelectron beam generator and the second end of the x-ray tube includingan anode having a surface upon which the electron beam is impinged togenerate a source of x-rays. The thermally-conductive, dielectricmaterial is typically thermally coupled to the anode. Cooling means mayalso be thermally coupled to the thermally-conductive, dielectricmaterial, for example, at least one cooling fin or cooling pin. In oneaspect of the invention, sufficient heat may be removed from the x-raytube by means of the thermally-conductive, dielectric material wherebythe x-ray tube assembly may be air cooled. In one aspect of theinvention, sufficient heat may be removed from the x-ray tube by meansof the thermally-conductive, dielectric material whereby the x-ray tubeis not contacted with a fluid coolant.

Another aspect of the invention comprises a method of operating an x-raytube assembly having an electron beam generator and an anode,comprising: directing a beam of electrons from the electron beamgenerator to the anode to generate x-rays and thereby heat the anode;providing a thermally-conductive, dielectric material thermally coupledwith the anode, and conducting heat from the anode by means of thethermally-conductive, dielectric material. Again, thethermally-conductive, dielectric material may be aluminum nitride,beryllium oxide, or diamond-like carbon, among others. In one aspect,the anode is electrically isolated and little or no electrons pass fromthe anode to the thermally-conductive, dielectric material. In oneaspect of this method, sufficient heat may be removed from the anodewhen conducting heat from the anode by means of thethermally-conductive, dielectric material whereby the x-ray tubeassembly may be air cooled. In one aspect of this method, sufficientheat may be removed from the anode when conducting heat from the anodeby means of the thermally-conductive, dielectric material whereby thex-ray tube is not contacted with a fluid coolant.

Another aspect of the invention comprises an x-ray source assembly,comprising: a housing; an x-ray tube for generating x-rays, the x-raytube being mounted in the housing; a thermally-conductive, dielectricmaterial thermally coupled to the x-ray tube for removing heat generatedby the x-ray tube; and at least one perforation in the housing foremitting x-rays generated by the x-ray tube. The x-ray source assemblymay further include means for adjustably mounting the x-ray tube in thehousing. In one aspect, the x-ray source assembly includes an x-ray tubehaving a first end and a second end and the first end of the x-ray tubecomprises an electron beam generator and the second end of the x-raytube comprises a surface upon which the electron beam is impinged togenerate the x-rays. Again, the thermally-conductive, dielectricmaterial may be aluminum nitride, beryllium oxide, or diamond-likecarbon, among others. The dielectric material may also be cooled by atleast one cooling fin or cooling pin thermally coupled to thethermally-conductive, dielectric material. The x-ray source assembly mayalso have an x-ray source which is adjustably mounted to the x-ray tubehousing, for example, by at least one threaded pin. The x-ray sourceassembly may also include means for varying or modifying the x-raysemitted through the at least one perforation in the housing, forexample, by means of a moveable baffle with at least one perforation. Inone aspect of the invention, an x-ray optic may be mounted to receive atleast some x-rays emitted through the at least one perforation in thehousing. In one aspect of this assembly, sufficient heat may be removedfrom the x-ray tube by means of the thermally-conductive, dielectricmaterial whereby the x-ray tube assembly may be air cooled. In oneaspect of this assembly, sufficient heat may be removed from the x-raytube by means of the thermally-conductive, dielectric material wherebythe x-ray tube is not contacted with a fluid coolant.

Another aspect of the present invention comprises a method of operatingan x-ray tube assembly having a first end comprising an electron beamgenerator and a second end having an anode and a thermally-conductive,dielectric material thermally coupled with the anode, comprising:directing a beam of electrons from the electron beam generator to theanode to provide x-rays and thereby heat the anode; and cooling theanode by conducting heat from the anode to the thermally-conductive,dielectric material. The x-ray tube assembly may also include at leastone cooling pin or cooling fin and cooling the anode may further includepassing a fluid coolant over the at least one cooling pin or coolingfin. Also, the cooling of the anode by conducting heat from the anode tothe thermally-conductive, dielectric material may be practiced whilepassing little or no electrons from the anode. In one aspect of thismethod, sufficient heat may be removed from the anode when cooling theanode by conducting heat from the anode by means of thethermally-conductive, dielectric material whereby the x-ray tubeassembly may be air-cooled. In another aspect of this method, sufficientheat may be removed from the anode when cooling the anode by conductingheat from the anode by means of the thermally-conductive, dielectricmaterial whereby the x-ray tube is not contacted with a fluid coolant.

Another aspect of the present invention comprises a method foroptimizing transmission of x-rays from an x-ray source and an x-rayfocusing device wherein the x-ray source comprises an x-ray tube forgenerating x-rays, the x-ray tube being mounted in a housing byadjustable mounting means, and the housing having at least oneperforation for emitting x-rays generated by the x-ray tube, the methodcomprising: mounting the x-ray tube in the housing; energizing the x-raytube whereby a beam of x-rays is emitted through the at least oneperforation in the housing; mounting the x-ray focusing device adjacentto the at least one perforation in the housing whereby the x-rayfocusing device receives at least some x-rays from the x-ray tube; andadjusting the adjustable mounting means of the x-ray tube to optimizetransmission of x-rays through the x-ray focusing device. The adjustablemounting means may comprise a plurality of threaded fasteners. The x-rayfocusing device may comprise an x-ray focusing crystal or an x-rayfocusing capillary device.

A further aspect of the present invention is an x-ray fluorescenceanalysis system, comprising: an x-ray source assembly having an x-raysource and a housing; a first x-ray focusing device operativelyconnected to the x-ray source assembly and having means for aligning thefirst x-ray focusing device with the x-ray source assembly; an x-rayexposure assembly having a housing operatively connected to the x-rayfocusing device and having means for aligning the x-ray exposureassembly with the first x-ray focusing device; a second x-ray focusingdevice operatively connected to the x-ray exposure assembly and havingmeans for aligning the second x-ray focusing device with the x-rayexposure assembly; and an x-ray detection device operatively connectedto the second x-ray focusing device and having means for aligning thex-ray detection device with the second x-ray focusing device; wherein atleast one of the means for aligning comprises a plurality of alignmentpins. The alignment of at least one of the assemblies, preferably aplurality of assemblies, permits one or more of the assemblies to beassembled off site and installed on site without requiring extensiverealignment of the assemblies on site. Avoiding realignment on site ismore efficient.

Another aspect of the present invention is a method of detecting x-rays,comprising: providing a source of x-rays; focusing at least some of thex-rays using an x-ray optic on a small-area x-ray detector; anddetecting the x-rays by means of the small-area x-ray detector. In oneaspect of the invention, the small-area detector may be may be asemiconductor-type detector or a silicon-lithium-type detector (that is,a SiLi-type detector). In one aspect of the invention, the small-aredetector may be a PIN-diode-type detector. One aspect of the inventionfurther comprises cooling the small-area detector, for example,air-cooling the small-area detector. The small-area ray detector mayinclude a detector aperture and the detector aperture area may be lessthan about 10 square millimeters, preferably, less than about 6 squaremillimeters, or even less than about 4 square millimeters. The focusingof at least some of the x-rays may be practiced using a capillary-typex-ray optic or a DCC x-ray optic. The method may be practiced at atemperature greater than about 0 degrees centigrade, for example, at atemperature between about 10 degrees centigrade and about 40 degreescentigrade.

A further aspect of the invention comprises a device for detectingx-rays, comprising: a small-area x-ray detector; and means for focusingat least some of the x-rays on small-area x-ray detector. The small-areax-ray detector typically includes a detector aperture having an arealess than about 10 square millimeters, typically, less than about 6square millimeters. The small-area x-ray detector may be asemiconductor-type detector or a silicon-lithium-type detector. In oneaspect of the invention the small-area detector may be a PIN-diode-type.In one aspect of the invention, the small-area detector may be cooled,for example, air-cooled. The means for focusing at least some x-rays maycomprise an x-ray optic, for example, a curved-crystal or capillaryx-ray optic.

Another aspect of the invention comprises an apparatus for analyzing afluid using x-rays, comprising: means for exposing the fluid to x-raysto cause at least one component of the fluid to x-ray fluoresce; andmeans for analyzing the x-ray fluorescence from the fluid to determineat least one characteristic of the fluid. The fluid may be a liquid or agas. The means for exposing the fluid to x-rays may be at least onex-ray optic for focusing x-rays on the fluid.

Another aspect of the present invention comprises a method for analyzingcomponents in a fluid using x-rays, comprising: exposing the fluid tox-rays to cause at least one component in the fluid to x-ray fluoresce;detecting the x-ray fluorescence from the fluid; and analyzing thedetected x-ray fluorescence to determine at least one characteristic ofthe fluid. According to one aspect, the method is practiced essentiallycontinually for a period of time. The method may also be practiced undervacuum.

In one aspect, the detecting of the x-ray fluorescence is practiced at atemperature greater than about minus 50 degrees centigrade, for example,at greater than about 0 degrees centigrade. In another aspect of themethod, the detecting of the x-ray fluorescence may be practiced using asmall-area x-ray detector, for instance, a semiconductor-type x-raydetector, for example, a PIN-type semiconductor x-ray detector.

Another aspect of the present invention comprises an apparatus foranalyzing sulfur in a fuel, comprising: means for exposing the fuel tox-rays to cause at least some sulfur in the fuel to x-ray fluoresce; andmeans for analyzing the x-ray fluorescence from the fuel to determine atleast one characteristic of the sulfur in the fuel. The at least onecharacteristic of the sulfur in the fuel may be the concentration ofsulfur in the fuel.

A still further aspect of the present invention is a method foranalyzing sulfur in a fuel, comprising: exposing the fuel to x-rays tocause at least some of the sulfur in the fuel to x-ray fluoresce;detecting the x-ray fluorescence; and analyzing the x-ray fluorescencefrom the sulfur to determine at least one characteristic of the sulfurin the fuel. The method is typically practiced essentially continuallyfor a period of time. The exposing of the fuel to x-rays may bepracticed under vacuum. When practiced under vacuum, the fuel willtypically be enclosed in a chamber to prevent exposure to the vacuum,for example, the fuel may be enclosed in a chamber and the x-rays accessthe fuel via a window in the chamber. According to one aspect, thex-rays may be monochromatic x-rays. Also, the detecting of the x-rayfluorescence may be practiced at a temperature greater than about minus100 degrees centigrade, typically greater than about minus 50 degreescentigrade, or even greater than about 0 degrees centigrade, for exampleat about room temperature (20 degrees centigrade). The detecting may bepracticed using a semiconductor-type detector, for example, a PIN-typesemiconductor detector.

Regarding improved heat dissipating aspects of the invention, theinvention is a device for cooling and electrically-insulating ahigh-voltage, heat-generating component. This device includes: a firstthermally-conductive material having a first side in thermalcommunication with the component and a second side; athermally-conductive dielectric material having a first side in thermalcommunication with the second side of the first thermally-conductivematerial and a second side; and a second thermally-conductive materialhaving a first side in thermal communication with the second side of thethermally-conductive, dielectric material; wherein heat generated by thecomponent is conducted away from the component through the device whilecurrent loss across the device is minimized. In one aspect of theinvention, the thermal communication between the component and the firstthermally-conductive material is through an area of contact between thecomponent and the first thermally-conductive material, the area ofcontact having a first outer dimension, and wherein the firstthermally-conductive material comprises a periphery having a secondouter dimension, greater than the first outer dimension, wherein atleast some heat from the component is conducted in the firstthermally-conductive material in a direction from the area of contacttoward the periphery of the first thermally-conductive material. Inanother aspect of the invention, the first thermally-conductive materialcomprises a first plate, wherein at least some heat is conducted in thefirst plate in a direction from the area of contact toward the peripheryof the first plate, and hence through the thermally-conductivedielectric material to the second thermally-conductive material. Theinvention may also include means for facilitating removal of heat fromthe second thermally-conductive material, for example, at least onecooling fin or cooling pin. In one aspect of the invention, thethermally-conductive dielectric material comprises one of aluminumnitride, beryllium oxide, and diamond-like carbon. The high-voltage,heat-generating component may be an x-ray generator, an electron-beamgenerator, a high-voltage lead, or a microwave generator, among otherdevices.

This aspect of the invention may be used with the fluid-analyzingtechnique and optics discussed above.

Another aspect of the heat dissipating invention is an x-ray tubeassembly including: an x-ray tube comprising a high-voltage, heatedanode; and a heat dissipating device coupled to the anode, the heatdissipating device comprising: a first metal plate having a first sidein thermal communication with the anode and a second side; athermally-conductive dielectric material plate having a first side inthermal communication with the second side of the first metal plate anda second side; and a second metal plate having a first side in thermalcommunication with the second side of the thermally-conductivedielectric material plate; wherein heat generated in the anode isconducted away from the anode through the device while current lossacross the device is minimized. In one enhanced aspect of the invention,the heat dissipating device provided structural support for the anode,for example, the heat dissipating device can provide essentially all thestructural support for the anode. In another aspect of the invention,the x-ray tube assembly further includes a high voltage connectorcoupled with the first metal plate.

This aspect of the invention may be used with the fluid-analyzingtechnique and optics discussed above.

A further aspect of the heat dissipation invention is a method forfabricating a device for cooling and electrically-insulating ahigh-voltage, heat-generating component, the method comprising:providing a first thermally-conductive material having a first surfacefor contacting the component and a second surface; providing athermally-conductive dielectric material having a first surface and asecond surface; coupling the first surface of the firstthermally-conductive dielectric material to the second surface of thefirst thermally-conductive material, so that the firstthermally-conductive material and the thermally-conductive dielectricmaterial are in thermal communication; providing a secondthermally-conductive material having a first surface and a secondsurface; and coupling the first surface of the secondthermally-conductive material to the second surface of thethermally-conductive dielectric material so that thethermally-conductive dielectric material and the secondthermally-conductive material are in thermal communication. In oneaspect of the invention, coupling comprises, gluing, adhesive bonding,soldering, brazing, or welding. One adhesive that may be used is DowChemical's 4174 thermally-conductive, silicone adhesive, or itsequivalent. Another aspect of the invention further includes coupling ahigh voltage connector to the electrically-conductive, firstthermally-conductive material.

This aspect of the invention may be used with the fluid-analyzing systemand optics discussed above.

Since it may be desirable to align the x-ray beam produced by an x-raydevice with an internal or external x-ray optic, according to one aspectof the invention, the components of an x-ray beam device are mounted ina way that enables the user to adjust the position or direction of thex-ray beam relative to an optic to account for, among other things,variations in alignment due to thermal expansion. Furthermore, since thealignment of an x-ray beam device with an optic can be difficult whenthe x-ray tube is bolted inside a sealed container and the sealedcontainer contains a cooling fluid, in one aspect of the invention,x-ray beam device is provided which requires little or no cooling fluid.For example, according to one aspect of the invention, an x-ray beamdevice is provided having sufficient cooling yet permitting alignment ofthe device, for example, precise alignment with an optical device.

This aspect of the invention may be used with the fluid-analyzing systemand optics discussed above.

Regarding the enhanced stability aspects of the invention, the use ofe-beam impingement upon an anode to generate x-rays, such as in thex-ray tubes described above, can generate an amount of heat that issufficient to cause thermal expansion of the elements which support andposition the x-ray tube within the x-ray source. This thermal expansioncan be sufficient to cause a misalignment between the x-rays that arediverging from the anode and, e.g., the element that serves to controlthe direction of the x-rays. As a result, operating an x-ray source atdifferent powers may lead to a range of misalignments between thediverging x-rays and the focusing electrode. This misalignment couldcause the output power intensity of the x-ray source to vary widely.Misalignment could also cause changes in x-ray spot or x-ray beamposition for some types of beam controlling elements, e.g., for pinholesor single reflection mirrors. Thus, in one aspect, provided herein is anx-ray source assembly having enhanced output stability over a range ofoperating power levels, as well as enhanced x-ray spot or x-ray beamposition stability. More particularly, an x-ray source assembly inaccordance with an aspect of the present invention provides an x-raybeam output intensity which can be maintained relatively constantnotwithstanding variation in one or more operating conditions of thex-ray source, such as anode power level, housing temperature and ambienttemperature about the assembly.

This aspect of the invention may be used with the fluid-analyzingsystem, optics and heat dissipation aspects discussed above.

For enhanced stability, additional advantages are provided through theprovision of an x-ray source assembly which includes an anode having asource spot upon which electrons impinge, and a control system forcontrolling position of the anode source spot relative to an outputstructure. The control system can maintain the anode source spotlocation relative to the output structure notwithstanding a change inone or more operating conditions of the x-ray source assembly.

This aspect of the invention may be used with the fluid-analyzingsystem, optics and heat dissipation aspects discussed above.

In another enhanced stability aspect of the invention, an x-ray sourceassembly is provided which includes an x-ray tube having an anode forgenerating x-rays, and an optic for collecting x-rays generated by theanode. The x-ray source assembly further includes a control system forcontrolling x-ray output intensity of the optic. The control system canmaintain x-ray output intensity notwithstanding a change in one or moreoperating conditions of the x-ray source assembly.

This aspect of the invention may be used with the fluid-analyzingsystem, optics and heat dissipation aspects discussed above.

In still another enhanced stability aspect of the invention, a method ofproviding x-rays is presented which includes: providing an x-ray sourceassembly having an anode with a source spot upon which electronsimpinge; and controlling position of the anode source spot relative toan output structure, wherein the controlling includes maintaining theanode source spot location relative to the output structurenotwithstanding a change in at least one operating condition of thex-ray source assembly.

This aspect of the invention may be used with the fluid-analyzingsystem, optics and heat dissipation aspects discussed above.

In a further enhanced stability aspect of the invention, a method ofproviding x-rays is presented which includes: providing an x-ray sourceassembly having an x-ray tube with an anode for generating x-rays and anoptic for collecting x-rays generated by the anode; and controllingx-ray output intensity from the optic, wherein the controlling includesmaintaining x-ray output intensity from the optic notwithstanding achange in at least one operating condition of the x-ray source assembly.

This aspect of the invention may be used with the fluid-analyzingsystem, optics and heat dissipation aspects discussed above.

These and other embodiments and aspects of the present invention willbecome more apparent upon review of the attached drawings, descriptionbelow, and attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the concluding portion of thespecification. The invention, however, both as to organization andmethod of practice, together with further objects and advantagesthereof, may best be understood by reference to the following detaileddescriptions of the preferred embodiments and the accompanying drawingsin which:

FIG. 1 is a schematic block diagram of an x-ray fluorescence system thatcan be used to practice the present invention.

FIG. 2 is a schematic cross-sectional view of a prior art x-ray tubeover which one aspect of the present invention is an improvement.

FIG. 3 is a schematic cross-sectional view of one aspect of the presentinvention.

FIGS. 4, 5, and 6 illustrate various perspective views of another aspectof the present invention.

FIG. 7 is a perspective view of the housing assembly of another aspectof the present invention.

FIG. 8 is a perspective view of the aspect of the invention shown inFIG. 7 with the housing removed.

FIG. 9 is a schematic block diagram of an x-ray fluorescence systemaccording to another aspect of the present invention.

FIG. 10 illustrates a cross-sectional elevation view of one embodimentof a high-voltage component and a cooling and electrically-insulatingdevice in accordance with one aspect of the present invention.

FIG. 11 illustrates a detail of the cooling and electrically-insulatingdevice of FIG. 10 in accordance with one aspect of the presentinvention.

FIG. 12 depicts a cross-sectional view of one embodiment of an x-raysource assembly, in accordance with an aspect of the present invention;

FIG. 13 depicts one example of a source scan curve for an x-ray sourcesuch as shown in FIG. 12 plotting output intensity versus displacement,in accordance with an aspect of the present invention;

FIG. 14 depicts a cross-sectional view of the x-ray source assembly ofFIG. 1 showing a source spot to optic misalignment, which is addressedin accordance with an aspect of the present invention;

FIG. 15 depicts a cross-sectional view of the x-ray source assembly ofFIG. 14 showing different sensor placements for monitoring source spotto optic displacement, in accordance with an aspect of the presentinvention;

FIG. 16 is a cross-sectional view of one embodiment of the anode baseassembly depicted in FIGS. 12, 14 & 15, in accordance with an aspect ofthe present invention;

FIG. 17 is a cross-sectional view of the anode stack of FIGS. 12, 14 &15, in accordance with an aspect of the present invention;

FIG. 17A is a graphical representation of change in temperature acrossthe elements of the anode stack for different anode power levels, inaccordance with an aspect of the present invention;

FIG. 17B is a graph of change in reference temperature as a function ofanode power level, in accordance with an aspect of the presentinvention;

FIG. 18 depicts a cross-sectional view of one embodiment of an enhancedx-ray source assembly, in accordance with an aspect of the presentinvention;

FIG. 19 depicts a block diagram of one embodiment of a control systemfor an x-ray source assembly, in accordance with an aspect of thepresent invention;

FIG. 19A is a representation of one embodiment of processing implementedby the processor of the control system of FIG. 19, in accordance with anaspect of the present invention;

FIG. 20 is a flowchart of one embodiment of control processing for anx-ray source assembly, in accordance with an aspect of the presentinvention; and

FIG. 21 is an exemplary reference temperature table which can beemployed by the control processing of FIG. 20, in accordance with anaspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a schematic block diagram of a typical system 10 usedfor exposing a substance to x-ray radiation to produce flourescentradiation which can then be detected and analyzed to determine acharacteristic of the substance. Such a system typically includes anx-ray source 12, a first x-ray focusing device 14, a sample excitationchamber 16, a second x-ray focusing device 18, and an x-ray detector 20.The x-ray source 12, for example, an x-ray tube, produces a beam ofx-rays 22. Since x-ray beam 22 is typically a divergent beam, beam 22 isdiffracted or focused by means of one or more x-ray focusing devices 14.X-ray focusing device 14 may be one or more doubly-curved crystals, forexample, a doubly-curved crystal having essentially parallel atomicplanes, such as the crystals disclosed in pending application Ser. No.09/667,966 filed on Sep. 22, 2000 (Atty. Ref. 0444.035), the disclosureof which is incorporated by reference herein. X-ray focusing device maybe one or more capillary-type x-ray optic or curved crystal optic, forexample, one of the optics disclosed in U.S. Pat. Nos. 6,317,483;6,285,506; 5,747,821; 5,745,547; 5,604,353; 5,570,408; 5,553,105;5,497,008; 5,192,869; and 5,175,755, the disclosures of which areincorporated by reference herein. The one or more x-ray focusing devicesproduces a focused beam 24 directed toward the sample excitation chamber16.

The sample under test in excitation chamber 16 may be any desiredsubstance for which a characteristic is desired. The sample may be asolid, a liquid or a gas. If the sample is a solid, the sample istypically located on a relatively flat surface, for example, an x-rayreflective flat surface, for example, an optically-reflective surface.The sample, if a solid, liquid, or gas, may also be contained in aclosed container or chamber, for example, a sealed container, having ax-ray transparent aperture through which x-ray beam can pass. Whenirradiated by beam 24, at least one of the constituents of sample inchamber 16 typically is excited in such a fashion that the constituentx-ray fluoresces, that is, produces a secondary source of x-rays 26 dueto excitation by x-rays 24. Again, since x-ray beam 26 is typically adiverging beam of x-rays, beam 26 is focused by means of the secondx-ray focusing device 18, for example, a device similar to device 14, toproduce a focused beam of x-rays 28 directed toward x-ray detector 20.It will be apparent to those of skill in the art that this and otheraspects of the present invention, though described with respect to x-rayfluorescence applications, may also be utilized in x-ray absorptionapplications.

X-ray detector 20 may be a proportional counter-type or a semiconductortype x-ray detector. Typically, x-ray detector 20 produces an electricalsignal 30 containing at least some characteristic of the detected x-rayswhich is forwarded to an analyzer 32 for analysis, printout, or otherdisplay.

Various aspects of the present invention provide advancements andimprovements to the system 10 and system components shown in FIG. 1. Oneof these aspects of the present invention is disclosed with respect toFIGS. 2 and 3. FIG. 2 illustrates a cross-section of a typical prior artx-ray tube assembly 34, for example, a Series 5000 TF5011 x-ray tubeproduced by Oxford Instruments of Scotts Valley, Calif., though othersimilar x-ray tubes may be used. As is typical, this prior art x-raytube 34 includes a cylindrical housing 36, which typically comprises anon-conducting glass housing. An electron-beam generator 38 and an anode40 are mounted in housing 34 typically in the orientation shown. Anode40 is typically a thin solid material, for example, tungsten or Chromiummounted on a conducting anode of copper or a similarhigh-thermal-conductivity material. Anode 40 is typically fashioned toprovide surface 50 and having cylindrical support structure 41 fashionedto provide a rigid support for anode 40 in housing 41 and also toisolate the gas volume above structure 41 from the volume belowstructure 41. Anode 40 also includes a cylindrical non-conductingsupport 44 which penetrates housing 36. Electrical connections 42provide power to the electron-beam generator 38. Housing 36 typicallyincludes at least one aperture 46 for emitting the x-rays produced byx-ray tube 34. Housing 36 typically isolates the internal volume of tube34 from the ambient environment and the internal volume of tube 34 istypically provided with at least some form or vacuum, for example, about10⁻⁶ Torr.

When power, for example, 50 Watts, is provided to electrical connections42, electron-beam generator 38 produces a beam of electrons, asindicated by arrow 48, directed towards surface 50 of anode 40. Surface50 is typically an inclined surface, for example, inclined at about 45degrees to the axis of the tube. The interaction of electron beam 48with surface 50 produces x-rays which are scattered in all directions.The wavelength and frequency of the x-rays produced is a function of thepower provided to electrical connections 42, among other things.However, at least one path of these scattered x-rays is indicated byarrow 52 directed toward aperture 46. The direction of x-ray beam 52 isa typically a function of the orientation of tube 34. The x-ray beamrepresented by arrow 52 passes through x-ray permeable barrier 54 inaperture 46. The x-ray permeable barrier 54 is typically made fromberyllium (Be) or titanium (Ti) which permits the passage of x-rayswhile isolating the internal volume of the housing 36 from the ambientenvironment.

The generation of x-rays by the impingement of electron beam 48 uponanode 40 generates substantial heat, for example, the temperature ofanode 40 typically is elevated to a least 60 degrees centigrade, and canreach as high as the melting point of tungsten. In consequence, tube 34is typically immersed in a cooling and insulating fluid 56, for example,an petroleum-based oil. Tube 34 and fluid 56 are typically contained ina cylindrical housing 58. Housing 58 is typically impermeable to x-rays,for example, housing 58 can be typically lead-lined. The volume ofcooling and insulating fluid 56 and thus the size of housing 58 is afunction of the cooling requirements of x-ray tube 34. Housing 58 alsotypically includes an aperture 60 aligned with aperture 46 of tube 34 toemit x-rays generated by tube 34. Tube 34 is typically rigidly mountedwithin housing 58 by means of a supporting structure 62 attached tosupport 44 of tube 34, for example, by means of a threaded connection.Support 44 is typically made of a non-conducting material, for example,a ceramic material, to electrically isolate anode 40 from housing 58.

FIG. 3 illustrates an x-ray tube assembly 64 according to one aspect ofthe present invention that is an improvement over the prior art x-raytube assembly illustrated in FIG. 2. Many of the features that appear inFIG. 3 can be essentially identical to the features of FIG. 2 and areidentified with the same reference numbers. According to this aspect ofthe present invention, x-ray tube assembly 64 includes an x-ray tube 34′(which may be similar to tube 34) having a housing 36, an electron-beamgenerator 38, an anode 40, and an aperture 46 essentially identical tothe structures illustrated and described with respect to FIG. 2.However, according to the present invention, x-ray tube assembly 64includes at least one thermally-conducting, but non-electricallyconducting material 70 mounted or thermally coupled to x-ray tube 34′.The thermally-conducting, non-electrically conducting material (whichmay be referred to as a thermally-conducting, dielectric material) 70 isa material having a high thermal conductivity and also a high dielectricstrength. For example, material 70 typically has a thermal conductivityof at least about 100 Wm-1K-1, and preferably at least 150 Wm⁻¹K⁻¹; andmaterial 70 typically has a dielectric strength of at least about1.6×10⁷Vm⁻¹, preferably at least about 2.56×10⁷Vm⁻¹. Material 70 may bealuminum nitride, beryllium oxide, diamond-like carbon, a combinationthereof, or equivalents or derivatives thereof, among others. In FIG. 3,material 70 is illustrated as a cylindrical structure, for example, acircular cylindrical or rectangular cylindrical structure, thoughmaterial 70 may take many difference geometrical shapes and provide thedesired function.

X-ray tube 64 may typically mounted in a housing 158. Housing 158, likehousing 58 in FIG. 2 is typically fabricated from an x-ray impermeablematerial, for example, a lead-lined material, lead, or tungsten. Housing158 may assume any appropriate shape, including circular cylindrical andrectangular cylindrical. In one aspect of the invention, housing 158 isfabricated from tungsten plate, and due to the poor machinability oftungsten, housing 158 is preferably rectangular cylindrical in shape. Ofcourse, should methods be produced for providing other means offabricating tungsten housings, these can also be applied to the presentinvention.

According to the present invention, thermally-conducting, dielectricmaterial 70 permits the conducting of heat away from anode 40specifically and tube 34′ in general while minimizing or preventing thepassage of electrical current from anode 40 specifically and tube 34′ ingeneral. In this aspect of the invention, support 44′ (unlike support 44of tube 34 of FIG. 2) is typically made of a conducting material, forexample, copper or aluminum. According to this aspect of the invention,heat is conducted away from anode 40 via support 44′ and material 70while material 70 electrically isolates anode 40 from, for example, anexternal housing 158.

Unlike prior art x-ray tube assemblies, the temperature of x-ray tube34′ according to this aspect of present invention can be reduced byconducting heat away from anode 40 and dissipating the heat to theadjacent environment via the surface area of material 70. Thus, material70 cools anode 40 specifically and tube 34′ in general such that thecooling requirements for tube 34′ are reduced, or increased heating ofanode 40 can be achieved. For example, in one aspect of the invention,the presence of material 70 provides sufficient means for cooling tube34′ whereby little or no additional cooling means is required. Inanother aspect of the invention, the presence of material 70 providessufficient means for cooling tube 34′ whereby air cooling providessufficient cooling of tube 34′, for example, forced air cooling (thoughnon-forced-air cooling characterizes one aspect of the invention). Inanother aspect of the invention, the presence of material 70 providessufficient means for cooling tube 34′ whereby less cooling andinsulating fluid is required than the fluid required for prior art x-raytube assemblies, for example, at least 10% less cooling fluid than priorart tube assemblies; typically, at least 20% less cooling fluid thanprior art tube assemblies; preferably, at least 50% less cooling fluidthan prior art tube assemblies.

According to one aspect of the present invention, the cooling capacityof material 70 is increased by increasing the surface area of material70, for example, by means of introducing cooling fins or cooling pins tomaterial 70. In another aspect of the invention, additional coolingcapacity is obtained by introducing cooling fins or cooling pins to astructure thermally coupled to material 70. One such optional structureis illustrated in phantom in FIG. 3. FIG. 3 includes plate 72 mounted orotherwise thermally coupled to material 70. Plate 72, made of athermally conductive material, for example copper or aluminum, mayprovide sufficient surface area for cooling. In this aspect of theinvention, the surface area of the thermally-coupled structure isenhanced by the use of cooling pins or cooling fins 74. According to oneaspect of the invention, plate 72 and fins 74 are comprised of amaterial that is thermally conductive so that heat can be conducted awayfrom material 70, for example, a copper-, iron, or aluminum-based. Inanother aspect of the invention, plate 72 is fabricated from a materialthat is both thermally conductive and resistant to the penetration ofx-rays, for example, tungsten-copper. The copper in tungsten-copperprovides the conductivity desired while the tungsten provides thedesired x-ray shielding. Other materials having the same or similarproperties may be used for plate 72. When plate 72 is a duplex materiallike tungsten-copper, fins 70 may be simply a copper- or aluminum-basedmaterial.

FIGS. 4, 5, and 6 illustrate an x-ray source and x-ray focusing deviceassembly 80 and an x-ray source assembly 82 according to other aspectsof the present invention. X-ray source and x-ray focusing deviceassembly 80 comprises x-ray source assembly 82 and x-ray focusing device84. The x-ray focusing device 84 shown in FIG. 4 is a polycapillaryx-ray optic as disclosed in above-referenced U.S. patents, but device 84may be any type of x-ray focusing device, for example, the x-rayfocusing crystals and capillary type optics discussed above. In oneaspect of the invention x-ray source assembly 82 comprises at least onex-ray source 64 having a thermally-conductive dielectric material 70 asdescribed and illustrated in FIG. 3. Though x-ray source assembly 82 isshown rectangular cylindrical in shape in FIG. 3, assembly 82 may takeany convenient geometric shape, including circular cylindrical orspherical. Assembly 82 receives electrical power via electricalconnections 86, 87.

FIG. 5 illustrates a cut-away view of x-ray source and x-ray focusingdevice assembly 80 shown in FIG. 4. As shown in FIG. 5, assembly 80includes x-ray source assembly 82 and x-ray focusing device 84. X-raysource assembly 82 includes a housing 88, an x-ray tube assembly 64 (asshown in FIG. 3) and an x-ray baffle assembly 90. According to thisaspect of the invention, housing 88 is cylindrical in shape, forexample, circular or rectangular cylindrical in shape, and fabricatedfrom a x-ray shielding material, for example, lead, a lead-linedmaterial, tungsten, depleted uranium, or combinations thereof. Housing88 includes at least one perforation (not shown) for emitting x-raysgenerated by x-ray tube 34′ and means 89 for mounting x-ray optic 84. Inthe aspect of the invention shown in FIG. 5, mounting means 89 comprisesa bolted flange connection positioned about the penetration in thehousing through which the x-rays generated by x-ray tube 34′ pass tooptic 84.

Housing 82 may also include a bottom plate 92 having a perforation 94through which x-ray tube assembly 64 may extend. For example, as shownin FIG. 5, the cooling fins 74 of x-ray tube assembly 64 may extendthrough bottom plate perforation 94, for example, to provide air accessto cooling fins 74. As shown, in one aspect of the invention coolingfins 74 may be radially directed.

According to another aspect of the present invention, housing 88preferably includes at least one means of aligning housing 88 to thecomponents to which it is mounted. For example, the aligning means inhousing 88 may include one or more dowel pins or dowel pin holes 98 thatare referenced to the orientation of the x-ray tube source spot. Theadjustment and orientation of these dowel holes or pins will bediscussed below.

X-ray source assembly 82 may also include a baffle plate assembly 90 forvarying the amount and type of x-rays emitted from assembly 82.According to this aspect of the invention, baffle assembly 90 includes abaffle cylinder 91 having at least one penetration 96, preferably aplurality of penetrations 96, which are translatable relative to thex-ray aperture in the x-ray tube assembly, for example, relative toaperture 46 shown in FIG. 3. Apertures 96 may vary in size and shape ormay contain one or more x-ray filtering devices that can be used to varythe amount and type of x-rays emitted by assembly 82. Though baffleassembly 90 may comprise any type of plate having one or more apertures,according to the aspect of the invention shown in FIG. 5, baffleassembly 90 comprises a circular cylinder 91 mounted about the axis ofx-ray tube 34′ and rotatably mounted to housing 88. Baffle cylinder 91may be mounted on disk 93. According to this aspect of the presentinvention, the orientation of apertures 96 relative to the aperture oftube 34′ (again see FIG. 3) may be varied by rotating baffle cylinder 91via disk 93 by means not shown. The means of rotating baffle cylinder 91may be manual means or automated means, for example, by means of astepper motor or linear actuator.

FIG. 6 illustrates a view of x-ray source and focusing device assembly80 of FIGS. 4 and 5 with the sides and top of housing 88 removed forclarity of illustration. FIG. 6 illustrates x-ray tube assembly 64,baffle cylinder assembly 90, and x-ray optic 84. FIG. 6 also illustratesthe adjustable mounting of x-ray tube assembly 64 onto the bottom plate92 of housing 88. As shown in FIG. 5, electrical connection 86 isoperatively connected to anode 40 of tube 34′ and electrical connection87 is operatively connected to electron-beam anode generator 38 of tube34′ (see FIG. 3).

According to this aspect of the invention, x-ray tube assembly 64(having thermal conductive, dielectric material 70) is adjustablymounted to housing 88 whereby the direction and orientation of thex-rays emitted by x-ray tube 34′ may be varied and optimized, forexample, optimized for alignment with x-ray optic 84. Though many meansof varying the orientation and alignment of x-ray tube assembly 64 maybe used, including rotational and transnational adjustment, according tothe aspect of the invention shown in FIGS. 4, 5, and 6, orientation andalignment of x-ray tube assembly 64 is effected by means of at least onethreaded rod or screw, preferably a plurality of threaded rods orscrews. In the aspect shown in FIG. 6, three threaded screws 100 arethreaded through bottom plate 92 and engage the bottom surface of plate72. Screws 100 may be threaded into holes, for example threaded holes inplate 72, or may simply bear against the bottom surface of plate 72. Theadjustment of screws 100 or any other means of adjustment may bepracticed manually or may be automated.

According to one aspect of the invention, the adjustment of theorientation or tube assembly 64 is registerable with the housing 88.That is, in one aspect of the invention, the orientation of the x-raybeam produced by x-ray tube 34′ is registerable to housing 88 and thealignment of components mating to x-ray source assembly 82. For example,x-ray focusing devices or sample excitation chamber, may be aligned tox-ray tube 34′ by simply aligning with one or more datum points on thehousing. In the aspect of the invention shown in FIGS. 4, 5, and 6, theorientation and alignment of the x-ray beam created by x-ray tube 34′ isregistered with the one or more dowel pins or dowel pin holes 98 onhousing 88. As a result, by appropriately aligning mating components todowel pins or holes 98, mating components can be accordingly alignedwith the x-ray beam of tube 34′, for example, with little or no furtheradjustment.

FIG. 7 illustrates an x-ray fluorescence assembly 110 according toanother aspect of this invention. X-ray fluorescence assembly 110comprises an x-ray source assembly 112, a sample excitation chamberassembly 116 and an x-ray detector assembly 120. Assembly 110 alsoincludes at least one x-ray focusing device (typically at least twodevices) which is not shown. All these devices are integrated into asingle assembly 110 having a housing 115.

FIG. 8 illustrates the x-ray fluorescence system 110 shown in FIG. 7,but with housing 115 removed to show the representative spatialrelationship between x-ray source assembly 112, sample excitationchamber assembly 116, x-ray detector assembly 120, and two x-rayfocusing devices 114, 118. In a fashion analogous to the system 10 shownin FIG. 1, x-ray source assembly 112 produces an x-ray beam 122 which isfocused by x-ray focusing device 114 to produce a focused beam 124 on asample under test in excitation chamber assembly 116. The x-rayfluorescence created by the x-ray irradiation of the sample in sampleexcitation chamber assembly 116 generates x-ray flourescent beam 126.Beam 126 is focused by x-ray focusing device 118 to provide a focusedx-ray beam 128 which is directed to x-ray detector assembly 120. Sourceassembly 112, holder assembly 116, and detector assembly each includemounting flanges 113, 117, and 121, respectively for mounting eachassembly to housing 115. X-ray focusing devices 114 and 118 also includemeans for mounting these device to housing 115.

In prior art methods of XRF detection, for example, in the D2622 method,the sample excitation path and detection path are maintained in an inertgas atmosphere, for example, in a helium atmosphere. However, theavailability of inert gases, especially in remote locations, makes theimplementation of these prior art processes inconvenient. In contrast,in one aspect of the present invention, the sample excitation path andthe detection path are maintained under vacuum and no inert gas isnecessary. For example, in system 110 shown in FIGS. 7 and 8, housing115 is held under vacuum, for example, at least about 15 torr. Vacuumcan be provided by a venturi pump having no moving parts. However, ifdesired and available, an in another aspect of the invention, an inertgas such as nitrogen or helium can be introduced and maintained inhousing 1115, for example, under pressure. In another aspect of theinvention, housing 115 may be heated or cooled, for example, heated orcooled by means of a direct or indirect heat exchanger or via radiant orconvective heating or cooling means. In another aspect of thisinvention, housing 115 may be unpressurized and contain essentiallyatmospheric pressure and temperature.

X-ray source assembly 112 may include any type of x-ray source, butsource assembly 112 preferably includes a source similar or identical tosource assembly 82 shown in FIGS. 4, 5, and 6. That is, source assembly112 preferably includes an x-ray tube assembly having athermally-conductive dielectric, such as material 70, and is adjustablymounted to its housing and is registerable to adjacent components, forexample, to housing 115 via dowel pins or dowel holes.

X-ray focusing devices 114 and 118 may be any one of the focusingdevices discussed previously, for example, a doubly-curved crystal or apolycapillary optic. Though x-ray focusing devices 114 and 118illustrated in FIG. 8 are shown as doubly-curved crystals, other typesof x-ray optics may also be used for system 110, includingpolycapillary, monolithic x-ray optics as disclosed in theabove-referenced U.S. patents.

In some prior art XRF methods (again, for example, the D2622 method) theexcitation of the sample is practiced using polychromatic x-rays. Amongother things, the use of polychromatic x-ray excitation requires the useof at least two x-ray wavelengths in order to correct for errorsinherent in polychromatic excitation. According to one aspect of thepresent invention, excitation, for example, by means of x-ray focusingdevice 114, is practiced using monochromatic x-rays. The use ofmonochromatic excitation avoids the need to correct detection errorswhich is typically required when using polychromatic excitation. Forexample, in one aspect of the present invention, background radiationlevels are reduced since there is no Bremsstrahlung illumination. As aresult, the present invention provides a higher signal to noise ratiothan prior art methods using polychromatic excitation.

X-ray sample excitation chamber assembly 116 may comprise any type ofcavity or surface for holding or retaining a sample for testing, forexample, a solid, liquid, or gas sample. In one aspect of the invention,sample excitation chamber assembly 116 includes conduits 123 and 125 forintroducing and removing, respectively, a sample from the sampleexcitation chamber 116, for, example, for continuous fluid (that is, gasor liquid) analysis.

Prior art XRF methods (for example, the D2622 method) typically requiresample sizes of at least 25 mm in diameter, often much larger. In oneaspect of the present invention, having an x-ray focusing device, thesample diameter may be less than 25 mm in diameter, even less than 10 mmin diameter, or even less than 3 mm in diameter. The capability to havesuch small sample diameters allows for smaller illumination areas andmore reliable excitation and detection.

X-ray detector assembly 120 may comprise any type of x-ray detectorcapable of receiving an x-ray beam 128, for example, a focused x-raybeam. Detector assembly 120 may include a proportional-counter typex-ray detector or a semiconductor type x-ray detector. In one aspect ofthe invention, x-ray detector 120 includes at least one PIN-diode-typex-ray detector.

Typical prior art XRF methods (again, for example, the D2622 method) useproportional counters for x-ray detectors. However, proportionalcounter-type detectors typically require large detection areas or longdetection times to count as many photons as possible. Also, proportionalcounter-type detectors typically have “windows” over their detectionareas. Though for high-energy x-rays the presence of the window isinconsequential, when low-energy x-rays are detected using aproportional counter-type detectors, the presence of the window caninterfere with the transmitted x-rays. Making the window thinner toavoid such interferences, increases the potential for gas leakage.However, in one aspect of the present invention, having excitationx-rays focused on the detector avoids the need for large detectionareas, long detection times, or windows which characterize proportionalcounter-type detectors.

Another type of detector used in prior art methods (such as the D2622method) use semiconductor-type detectors. Semiconductor-type detectorsare typically preferred over proportion-counter-type detectors because,among other things, semiconductor-type detectors are smaller in size.For example, proportion-counter-type detectors typically have detectorareas about 500 times larger than the detector areas ofsemiconductor-type detectors. In addition, semiconductor-type detectorsachieve higher resolutions and better distinguish x-ray energies thanproportional-counter-type detectors. However, semiconductor-typedetectors are typically limited in size because as the size of thesemiconductor-type detector increases, the semiconductor “leakagecurrent” increases producing undesirable detection noise. On the otherhand, reducing the size of semiconductor-type detectors reducesdetection noise due to leakage current. However, typically,semiconductor-type detectors are also limited in how small a detectorcan be since detector detection efficiency begins to decline as thesemiconductor-type detector gets smaller.

Typically, to increase the performance of semiconductor-type detectors,the semiconductor type devices are cooled, for example, cooled anywherefrom about minus 10 degrees C. to about 77 degrees Kelvin. However,cooling such devices is expensive and inconvenient. In addition, coolingsemiconductor-type detectors introduces the potential to formcondensation on the detector which interferes with detector performance.One method of reducing the potential for condensation to form on acooled detector is to maintain the detector behind a window in a inertgas environment, for example, using nitrogen. Sometimes a vacuum is usedinstead of an insert gas to limit the heat transfer present due to theinert gas. However, again, the use of inert gases or vacuum for asemiconductor-type detector is inconvenient and expensive and preferablyis avoided.

Some of the shortcomings of the use of semiconductor-type detector areavoided or overcome by the present invention. First, due to the focusingof the excitation beam using x-ray focusing devices, the large detectionareas of the proportional-counter-type detectors are avoided. Thefocusing of x-rays according to the present invention is more amenableto semiconductor-type detectors. The focusing and concentration of x-rayenergy or flux according to the present invention, especially the use ofmonochromatic x-rays, somewhat counteracts the loss in resolution thattypically occurs as the size of semiconductor-type detectors decrease.As a result, according to one aspect of the present invention, asemiconductor type detector can be operated at temperatures greater than−10 degrees centigrade, for example, greater than 0 degrees centigrade,or greater than 10 degrees centigrade, or even at about room temperature(about 20 degrees centigrade) or above, with little appreciable loss inperformance, for example, compared to the performance of a proportionalcounter-type detector.

In addition, without the need for cooling, which typically requires someform of protective “window” in order to avoid condensation on the cooledsurface, according to one aspect of the present invention, no protectivewindow is required. That is, one aspect of the present invention is awindowless semiconductor-type x-ray detector for use at a temperatureabove 0 degrees centigrade or at about room temperature or above.

One type of semiconductor-type detector that can be used in an x-rayfluorescence system is a PIN-diode type semiconductor detector, forexample, a Silicon-PIN-diode. The specifications for one such PIN-diodedetector according to one aspect of the present invention appear inTable 1. The PIN-diode according to the present invention may be mountedto a pre-amplifier board and attached to an amplifier by means of acable. TABLE I PIN-diode-type X-ray Detector Specifications Type Si-PINActive area (diode) 2.4 mm × 2.4 mm (5.6 mm²) Thickness (diode) 500 μmDetector window 8 μm DuraBeryllium Detector housing TO-8 header 0.600inch diameter Collimator Type 0.060 inch Aluminum Detector Pre-amplifierwith 2 inch × 1 inch circuit board Detector Amplifier Board 3 inch × 5inch circuit board Cable Length 0 to 6 feet Detector Resolution, Mn Kα500 eV (typical) at 25 degrees C. (⁵⁵FE) Detector Resolution, Mn Kα 700eV (typical) at 40 degrees C. (⁵⁵FE) Peek to Background to be determinedEnergy conversion 5 mV/KeV (Typical); 10 mV/KeV (Max.) Lowest Detectionlimits 1 KeV Peak Shift 2% at a temp. betw. 25-40 degrees C. Noisecounts <0.01 cps at a temp. of 25 degrees C. Power Supply Input +/−12 V(Typical) Low Level Discriminator 0 V (Min.) 9 V (Max.) High LevelDiscriminator 0 V (Min.) 9 V (Max.) Energy Out Pulse 9 V (Max.) TTL OutPulse 5 V (Typical)

FIG. 9 illustrates an x-ray fluorescence system 210 for analyzingfluids, typically continuously, according to another aspect of thepresent invention. X-ray fluorescence analyzing system 210 typicallycomprises at least one x-ray fluorescence assembly 212, for example, thex-ray fluorescence system 110 shown in FIGS. 7 and 8, having an x-raysource assembly 112, an x-ray sample excitation chamber assembly 116, anx-ray detector assembly 120 and one or more x-ray focusing devices 114,118, though other assemblies performing similar functions may be used.System 210 also includes a fluid inlet 214, a fluid outlet 216, and afluid purge inlet 218. Inlet 214, outlet 216 and purge inlet 218 mayalso include manually or automatic isolation valves (not shown). Thefluid introduced to fluid inlet 214 may by any type of liquid or gasthat can be analyzed via x-ray fluorescence, but in one aspect of theinvention the fluid is a fuel, for example, a fluid fuel, such as apetroleum-based fuel, for example, gasoline, diesel fuel, propane,methane, butane, or coal gas, among others. One constituent ofpetroleum-based fuels that can be detected via x-ray fluorescence issulfur, though other constituents can also be detected. In one aspect ofthe invention, the fluid analyzed by system 210 is diesel fuel in whichthe content of sulfur in the diesel fuel is characterized, for example,the concentration of the sulfur is determined. A system forcharacterizing the sulfur content in diesel fuel is marketed under thetrademark SINDIE™ by X-Ray Optical Systems, Inc. of Albany, N.Y.

The flow of fluids through 210 is regulated and monitored by means ofvarious conventional flow and pressure control devices, for example, oneor more control valves 222, 224, flow meters, 226, and pressureindicators 228. Control valves 222, 224 are typically two- or three-wayvalves and may be manual or automated control valves. The control andoperation of system 220 may be manually controlled or automaticallycontrolled via controller 220. Controller 220 typically contains one ormore conventional Programable Logic Controllers (PLC), power inputs,power conditioners, signal inputs, signal processors, data analyzers,input devices and output devices. Controller 220 receives input signalsfrom and directs appropriate control systems to the monitoring andcontrol devices via the various electrical connections shown in phantomin FIG. 9. System 210 can be housed in one or more cabinets, housings,or enclosures 230, for example, the fluid handling devices may belocated in one cabinet and the controller 220 located in a separatecabinet. The cabinet or enclosure is typically a NEMA 4/12 purgedenclosure. System 210 may be stationary or portable.

The following description will specifically describe the application ofthe present invention for the detection of sulfur in diesel fuel, thatis, the SINDIE™ System, but it will be apparent to those of skill in theart that the present invention is applicable to other constituents ofdiesel fuel or to other fluids containing sulfur or other constituents.The operation of system 210 proceeds as follows. The x-ray analysisassembly 212 is energized, for example, via electrical connection 211from controller 220. Diesel fuel, typically containing at least somesulfur, is introduced to system 210 via inlet 214 and passes throughvalve 224 and into x-ray analysis assembly 212 via conduit 215. Thediesel fuel is introduced to the x-ray exposure chamber of x-rayexposure assembly in system 212 (for example, via conduit 123 in FIG. 8)where the diesel fuel is exposed to x-rays and at least some of thesulfur x-ray fluoresces and the presence of sulfur is detected by system212. An electrical signal corresponding the sulfur detected by system212 is transmitted to controller 220 for data analyses and or display.The diesel fuel exits the exposure chamber (for example, via conduit 125in FIG. 8) and passes through conduit 217 and is discharged from system210 via outlet 216. The pressure and rate of flow of fuel in conduit 217may be detected, respectively, by flow measuring device 226 (forexample, a rotometer) and pressure indicator 228 (for example, apressure gauge) and corresponding signals forwarded to controller 220via electrical connections 227 and 228, respectively. The direction offlow through (and the flow rate through) valves 222 and 224 may beregulated by controller 220 via control signals 223 and 225,respectively, for example, in response to the flow and pressure detectedby flowmeter 226 or pressure indicator 228. Purge inlet 218 may be usedto introduce a liquid or gas purge to the system, for example, water,air, or nitrogen, or to introduce fuels having known sulfur content forsystem calibration. The direction and flow of purge can be controlledeither manually or automatically via valves 222 and 224.

Again, it will be apparent to those of skill in the art that the compactand robust design of system 210, that is, the SINDIE™ System, isamenable to the analysis of many types of fluids. However, when used foranalyzing petroleum-based fuels, system 210 can be use for sulfuranalysis at the crude oil well, at the oil storage facilities, in fuelrefineries, anywhere in the fuel distribution pipeline or network, oranywhere else where the sulfur content of a petroleum-based fuel isdesired. The use of system 210 eliminates the need for samplepreparation and analytical reagents as is typically required inconventional methods of sulfur analysis of fuels. System 210 providescontinuous, rapid, on-line fuel sulfur content so that a qualityassessment and control can be effected as quickly as possible. Some ofthe analytical and physical specifications for the system shown in FIG.9 appear in Table II. TABLE II Analytical and Physical Specificationsfor the Aspect of the Invention Shown in FIG. 9 Detection Range 5 ppm(mg/kg) to 50,000 ppm Limit of Detection 1 ppm (typical) Repeatablity 5%RSD (10-200 ppm) Operating Temperature minus 18 to 50 degrees C.Communications RS 232/485 serial output base 10T/Ethernet Device NetProfibus-DP and optional DCS system Remote Diagnostic Capabilities YesMaximum input fuel stream 100 PSIG pressure Nitrogen Gas Purge Dry, at80-100 PSIG Power 110 VAC 50/60 Hz, 500 Watts Weight 250 lbs. (approx.)Dimensions 78 inches H × 24 inches W × 18 inches D

Improved Heat Dissipating Aspects of the Invention

In accordance with a further heat dissipating aspect of the presentinvention, FIG. 10 illustrates a cross-sectional view of an x-ray beamassembly 1100 having a high-dielectric-strength and thermally-conductivecooling and electrically-insulating device, in accordance with oneaspect of the invention. X-ray beam assembly 1100 includes an x-rayimpermeable enclosure 1160 containing a vacuum-tight x-ray tube 1105typically formed of glass or ceramic that has a transmission window1110. In FIG. 10, enclosure 1160 is only shown partially, but it is tobe understood that enclosure 1160 typically may surround the entirex-ray beam assembly 1100. X-ray tube 1105 houses an electron gun 1115arranged opposite a high-voltage (HV) anode 1125. Electron gun 1115 is adevice that, due to a voltage gradient, emits electrons in the form ofan electron stream, that is, an electron beam (e-beam) 1120, as is wellknown in the art. HV anode 1125 acts as a target upon which an electronstream impinges and as a result produces x-ray radiation 1130, that is,x-rays, as is also well-known in the art.

Electron gun 1115 is typically held at ground potential (for example,about zero volts) and HV anode 1125 is held at a high voltage potential,typically, at about 50 kv or above. As a result, the e-beam 1120, whichis emitting from electron gun 1115 at ground potential, is electricallyattracted to the surface of HV anode 1125, which is at high voltagepotential, thereby producing x-rays 1130. E-beam 1120 impinges anode1125 and X-rays 1130 are emitted from anode 1125 from a location onanode 1125 referred to as the “focal spot” 1127 of the x-rays 1130. Theangle of orientation of the surface of anode 1125 at focal spot 1127allows x-rays 1130 to be directed toward transmission window 1110.Transmission window 1110 is typically formed of an x-ray transmissivematerial, such as beryllium (Be), or the like, which allows x-rays 1130to exit x-ray beam assembly 1100, while maintaining the vacuum withinx-ray tube 1105. In one aspect of the invention, for example, whenhigher energy x-rays are used, for instance, 20 Kev photons or higher,no window may be needed, the x-rays may pass through the x-ray tube, forexample, a glass x-ray tube, without the need for a window.

The end of HV anode 1125 opposite the impingement surface typicallyprotrudes through the body of x-ray tube 1105 and is mechanically,thermally, or electrically coupled (for example, connected) to a baseassembly 1135. According to one aspect of the invention, base assembly1135 is a three-plate structure that includes a first plate 1140 madefrom a thermally-conductive material, a second plate 1150 made from adielectric material, and third plate, or base plate, 1145 made from athermally-conductive material. First plate 1140 is at least partiallyelectrically isolated from third plate 1145 by means of second,dielectric plate 1150. In one aspect of the invention, first plate 1140functions as a thermal spreader, that is, plate 1140 receives heat fromanode 1125 over a limited area, for example, a small centrally-locatedlimited area on plate 1140, and distributes the heat to a larger area ofplate 1140 to facilitate further dissipation of the heat. Base assembly1135 may be mounted to housing 1160. In one aspect of the invention,base assembly 1135 supports at least anode 1125 and may support x-raytube 1105. In one aspect of the invention, plate 1140 and anode 1125comprise a single integral component, for example, a component machinedfrom a single piece of metal or forged as a single component. In anotheraspect of the invention, plate 1140 and anode 1125 are separatecomponents which are mated by conventional means, for example, bysoldering, brazing, welding, or by means of an adhesive, for example, anelectrically conductive adhesive. In one aspect of the invention, baseassembly 1135 provides the only structural support for x-ray tube 1105.Further details of the interconnections within base assembly 1135 areprovided in FIG. 11.

In one aspect of the invention, plate 1140, plate 1145, or both plates1140 and 1145 may comprise a coating or layer of conductive material onplate 1150 (or on a similar structure, such as, a bar, block, orcylinder). In one aspect of the invention, the coating or layer ofconductive material corresponding to plate 1140, plate 1145, or bothplates 1140 and 1145 may comprise a layer of conductive material (forexample, copper, etc.) disposed on or applied to plate 1150 (or asimilar structure) by chemical vapor deposition or sputtering, amongother methods.

According to another aspect of the invention, base assembly 1135 maycomprise a single plate or component structure, for example, a singleplate 1150 (or similar structure, such as, a bar, block, or cylinder)made of a thermally-conductive dielectric material, and plate 1140 andplate 1145, or corresponding structures, may be omitted. Plate 1150 maybe disposed directly on anode 1125 and provide a sufficient thermal pathfor cooling anode 1125.

In another aspect of the invention, base assembly 1135 may comprise atwo-plate or two-member structure in which plate 1140 or plate 1145 (orequivalent structures) may be omitted. In one aspect of the invention,anode 1125 may be disposed on a thermally-conductive dielectric materialsuch as plate 1150 (or on a similar structure, such as, a bar, block, orcylinder) and electrically-conductive plate 1145 may be disposed onplate 1150 (or on a similar structure) and provide a sufficient thermalpath for cooling anode 1125. In one aspect of the invention, thefunction of electrically-conductive plate 1145 (or its equivalent) maybe provided by a layer or coating of conductive material applied to athermally-conductive dielectric material, such as plate 1150 (or asimilar structure). In one aspect of the invention, the layer or coatingof conductive material (for example, copper) may be applied by chemicalvapor deposition, sputtering, or similar processes. In one aspect of theinvention, the function of thermally-conductive, dielectric plate 1150may be provided by a layer or coating of thermally-conductive dielectricmaterial applied to conductive plate 1145 (or its equivalent). In oneaspect of the invention, the layer or coating of thermally-conductivedielectric material may be a diamond-like carbon (DLC), for example, aDLC applied to plate 1145 (or its equivalent) by means of chemical vapordeposition. In one aspect of the invention, the layer or coating ofthermally-conductive dielectric material acts as a thermal spreader todistribute heat from anode 1125 to conductor plate 1145.

In addition, in another two-component aspect of the invention, anode1125 may be disposed on a thermally-conductive, electrically-conductivematerial, such as plate 1140 (or on similar structure, such as, a bar,block, or cylinder) and a thermally-conductive, dielectric material(such as plate 1150 or similar structure) may be disposed on plate 1140(or on a similar structure) and provide a sufficient thermal path forcooling anode 1125. Again, in one aspect of the invention, the functionof electrically-conductive plate 1140 (or its equivalent) may beprovided by a layer of conductive material applied tothermally-conductive dielectric material such as plate 1150 (or on asimilar structure).

In the double- and triple-component embodiments of the invention, plates1140 and 1145 may be circular plates, for example, 2-inch diameterdisk-shaped plates, though any conventionally-shaped plates, forexample, triangular, square, or rectangular, may be used according tothe invention. Plates 1140 and 1145 may be formed from athermally-conductive material, for example, a highlythermally-conductive material, such as a copper-containing material, forinstance, copper; an aluminum-containing material; a silver-containingmaterial; a gold-containing material; a diamond material, for instancediamond-like carbon; or a combination of two or more of these materials.In one aspect of the invention, plates 1140 and 1145 may also comprisean electrically-conductive material, for example, one of the materialsmentioned above. Plates 1140 and 1145 may have a thickness in the rangeof about 0.1 inches to about 0.5 inches, for example, a thickness ofabout 0.25 inches. In one aspect of the invention, plates 1140 and 1145are about the same size, for example, may have about the same diameter.However, in one aspect of the invention, plates 1140 and 1145 are sizeddifferently, for example, as shown in FIG. 10 plate 1145 may be largerin than plate 1140, for instance, larger in diameter. Base plate 1145may also include some constructional or mounting arrangement to supportand accommodate the overall structure of x-ray beam assembly 1100. Inone aspect of the invention, the thickness of plate 1140, and of plate1145, may be small compared to the surface area of plate 1140. Forexample, in one aspect of the invention, the ratio of the surface area(in square inches) to the thickness of plate 1140, or plate 1145, (ininches) may typically be at least about 5 to 1. In one aspect of theinvention, the ratio of the surface area of plate 1140, or plate 1145,to its thickness may be between about 10 to 1 and about 100 to 1. In oneaspect of the invention, the diameter of plate 1140 is about 2 inchesand the thickness of plate 1140 is about 0.25 inches, which correspondsto an area to thickness ratio of about 12.5 to 1.

In the single-, double-, and triple-component embodiments of theinvention, dielectric plate 1150 may also be a circular plate, thoughany conventionally-shaped plate may be used, as described above withrespect to plates 1140 and 1145. Plate 1150 may be smaller than plates1140 and 1145, for example, when plates 1140, 1145, and 1150 arecircular in shape, plate 1150 may be smaller in diameter than plates1140 and 1145. In one aspect of the invention, plate 1150 may bedisk-shaped and about 1.5 inches in diameter. Plate 1150 may be formedfrom a material that provides high thermal conductivity at highvoltages, such as a beryllium oxide ceramic, an aluminum nitrideceramic, a diamond-like carbon, or their derivatives or equivalents. Asa result, dielectric plate 1150 may have a high dielectric strengthwhile also being a good thermal conductor. For example, in one aspect ofthe invention, dielectric plate 1150 comprises a material having athermally conductivity of at least about 150 Watts per meter per degreeK (W/m/K) and a dielectric strength of at least about 1.6×107 volts permeter (V/m). Dielectric plate 1150 may have a typical thickness in therange of between about 0.1 inches and about 0.5 inches, for example, athickness of about 0.25 inches. In one aspect of the invention, thethickness of dielectric plate 1150 may be small compared to the surfacearea of dielectric plate 1150. For example, in one aspect of theinvention, the ratio of the surface area (in square inches) to thethickness (in inches) of plate 1150 may typically be at least about 5to 1. In one aspect of the invention, the ratio of the surface area ofdielectric plate 1150 to its thickness may be between about 5 to 1 andabout 100 to 1. In one aspect of the invention, the diameter of plate1150 has a diameter of about 1.5 inches and a thickness of about 0.25inches which corresponds to an area to thickness ratio of about 7.0 to1.

Beryllium oxide ceramic has a typical thermal conductivity that is about⅔ that of copper while aluminum nitride ceramic has a thermalconductivity that is about ½ that of copper. In one aspect of theinvention, beryllium oxide ceramic is used for forming dielectric plate1150. In another aspect of the invention, aluminum nitride ceramic isused for forming dielectric plate 1150. In some applications, aluminumnitride ceramic is preferred because beryllium oxide is a toxicsubstance and is therefore not as desirable for a manufacturing processor for environmental reasons. In contrast, aluminum nitride ceramic is acost-effective, non-toxic alternative to beryllium oxide that is easy towork with.

In one aspect of the invention, the conductor plates 1140, 1145 and thedielectric plate 1150 are flat to minimize the amount of bondingmaterial between the plates. For example, in one aspect of theinvention, the surfaces of disks 1140 and 1145 and the surfaces of disk1150 are flat to within at least about 0.001 inches.

In one aspect of the invention, HV anode 1125 is at least thermallyconnected to plate 1140. In another aspect of the invention, anode 1150is at least thermally and electrically connected to plate 1140. In stillanother aspect of the invention, anode 1125 is mechanically, thermally,and electrically connected to plate 1140 of base assembly 1135. Inanother aspect of the invention, plate 1140 may be at least electricallyconnected to a high voltage source, for example, via a HV lead 1155. Inanother aspect of the invention, plate 1140 is mechanically, thermally,and electrically connected to a high voltage source, for example, via HVlead 1155. HV lead 1155 may be attached to plate 140 as disclosed incopending application Ser. No. 10/206,531 filed on Jul. 26, 2002, thatis, filed on the same day as the present application (Attrny. ref.0444.058), the disclosure of which is incorporated by reference herein.As a result, in one aspect of the invention, the high voltage potentialis supplied to plate 1140 and also to HV anode 1125. Conversely, baseplate 1145 is typically held at about ground potential. In one aspect ofthe invention, dielectric plate 1150 provides electrical isolationbetween the high-voltage plate 1140 and the grounded base plate 1145.Again, further details of all interconnections are provided below withreference to FIG. 11.

In another aspect of the invention, high-voltage cable 1155 mayelectrically communicate with anode 1125 by means other than via plate1140. For example, in one aspect of the invention, cable 1155 isdirectly connected to anode 1125, for example, by means of theelectrical connection disclosed in copending application Ser. No.10/206,531 (attrny. reference 0444.058). For example, in one aspect ofthe invention, in which anode 1125 is disposed directly on athermally-conductive dielectric material, such as plate 1150, cable 1155may be connected directly to anode 1125. In another aspect of theinvention, cable 1155 communicates with anode 1125 via other means, forexample, means not related to structure 1135.

In one aspect of the invention, the x-ray tube 1105 with electron gun1115 and HV anode 1125, base assembly 1135, and HV lead 1155, are housedin an enclosure 1160, thereby forming x-ray beam assembly 1100.Enclosure 1160 may be filled with an encapsulating material, also knownas an encapsulant, 1162, for example, a potting material, such as asilicone potting material or its equivalent, which encapsulates theelements of x-ray beam assembly 1100. As shown in FIG. 10, some elementsof the x-ray beam assembly 1100 may protrude beyond enclosure 1160, suchas base assembly 1135. Enclosure 1160 encapsulant 1162 may form astructure that may be void of air pockets and may serve to isolate manysurfaces of x-ray beam assembly 1100 from the ambient environment, forexample, ambient air, via encapsulant 1162 or housing 1160. In oneaspect of the invention, encapsulant 1162 comprises a material having abreakdown voltage of least about 1.6×10⁷ V/m, for example, a siliconepotting material or its equivalent. In another aspect of the invention,the thermal properties of encapsulant 1162 may not be critical to thefunction of encapsulant 1162, for example, the material comprisingencapsulant 1162 may not need be a good conductor of heat. One materialthat may be used for encapsulant 1162 is a silicone material, forexample, a silicone elastomer, such as Dow Sylgard® 184 siliconeelastomer, or its equivalent.

FIG. 11 illustrates a detailed cross-sectional view of base assembly1135 according to one aspect of the present invention. In one aspect ofthe invention, base assembly 1135 serves as a high-dielectric-strengthand thermally-conductive heat dissipating device. In another aspect ofthe invention, base assembly 1135 serves as a high-dielectric-strengthand thermally-conductive heat dissipating device and a structuralsupport for x-ray beam assembly 1100.

FIG. 11 illustrates that HV anode 1125 is at least thermally connectedto plate 1140, though in one aspect of the invention, anode 1125 ismechanically, thermally, and electrically connected to plate 1140. Inone aspect of the invention, anode 1125 is mechanically connected toplate 1140 via conventional means, for example, one or more mechanicalfasteners, welding, brazing, soldering, adhesives, and the like. In oneaspect of the invention, anode 1125 is connected to plate 1140 via amounting stud 1205, a bonding layer 1210, or a combination thereof.Mounting stud 1205 may be a threaded stud formed from a conductivematerial, for example, steel, aluminum, copper, or one of the otherconductive materials mentioned above. In the aspect of the inventionshown in FIG. 11, mounting stud 1205 threads into both the HV anode 1125and plate 1140. Bonding layer 1210 may be formed from, for example, ahigh-conductivity solder, such as, an indium-tin (In-Sn) solder, forinstance, an In-Sn Eutectic solder, or its equivalent.

Plates 1140, 1145, and 1150 may also be connected to each other byconventional means, for example, using one or more mechanical fasteners,welding, brazing, soldering, adhesives, and the like. In one aspect ofthe invention, dielectric plate 1150 is connected to plate 1140 andplate 1145 is connected to dielectric plate 1150 via bonding layers1215, 1220, respectively. Bonding layers 1215, 1220 may, for example, bea high-conductivity solder similar to the solder used for bonding layer1210 described above. In one aspect of the invention, plate 1145includes a means for supporting or mounting base assembly 1135, whichmay also support x-ray beam assembly 1100, or at least anode 1125.Though the means for supporting base assembly 1135 may be anyconventional support means, in one aspect of the invention, plate 1145includes at least one mounting hole 1405, for example, at least onethreaded mounting hole.

X-ray beam assembly 1100 may include further means for conducting anddissipating heat from plate 1145. In one aspect of the invention, plate1145 may be operatively connected to conventional means for conductingand dissipating heat from plate 1145. For example, plate 1145 may beoperatively connected to one or more cooling fins or cooling pins. Inanother aspect of the invention, plate 1145 or the cooling fins orcooling pins may also be exposed to forced air cooling, for example, bymeans of a fan, for instance an electric fan mounted to x-ray beamassembly 1100.

According to one aspect of the invention, plates 1140 and 1145 comprisesmooth edges, for example, radiused edges as shown in FIG. 11. Accordingto this aspect of the invention, the radiused edges minimize theelectric field gradients about the edges of the plates so as to reducethe potential for electric discharge between plates 1140 and 1145.

According to one aspect of the invention, base assembly 1135 providesmechanical support for x-ray beam assembly 1100, in particular supportfor high-voltage anode 1125, for example, with little or no directsupport from the low voltage or grounded components of x-ray beamassembly 1100. According to one aspect of the invention, the mechanicalsupport provided by base assembly 1135 also includes a thermalconduction path for removing heat from x-ray beam assembly 1100. Inanother aspect of the invention, in addition to mechanical support andthermal conduction, base assembly 1135 may also provide at least someelectrical isolation, wherein little or no current is lost over baseassembly 1135, that is, current loss from anode 1125, or from any otherhigh-voltage components of x-ray beam assembly 1100, is minimized.

According to another aspect of the present invention, base assembly 1135provides an effective mean of dissipating, for example, conducting, heatfrom x-ray beam assembly 1100, for example, from anode 1125. Accordingto this aspect of the invention (see FIG. 10), heat generated by theimpingement of beam 1120 on anode 1125 and the generation of x-rays 1130is conducted from point of impingement 1127 along anode 1125 and intoplate 1140. Plate 1140 then conducts heat from the point of contact ofanode 1125, for example, in a radial direction, and distributes the heatto plate 1140, for example, uniformly distributes heat to plate 1140.The heat in plate 1140 is then conducted into plate 1150 and from plate1150 the heat is conducted in plate 1145. According to one aspect of theinvention, the distribution of heat in plate 1140 effectivelydistributes the heat in plate 1140 wherein the temperature differenceacross dielectric plate 1150 is minimized. As a result, the thermalconductivity of dielectric plate 1150 may be less than the conductivelyof conventional conducting materials, for example copper-containingmaterials, and still provide sufficient conductivity to dissipate heatfrom plate 1140 to plate 1145. The heat in plate 1145 may be furtherdissipated through conduction to mating structures or through naturalconvection, forced air convection, or flowing a cooling fluid over plate1145. In one aspect of the invention, cooling pins or fins (not shown)may be attached to be operatively connected to plate 1145. In addition,according to one aspect of the invention, one or more dielectric plates1150 and conducting plates 1145 may be mounted to plate 1140, forexample, 2 or more sets of plates 1150 and 1145 may be used to conductheat away from x-ray beam assembly 1100.

According to one aspect of the invention, an x-ray producing device isprovided which requires little or no cooling fluids, for example, littleor no internal cooling fluids. That is, one aspect of the invention,obviates the need to provide sealing means, leakage prevention, orreplacement fluids that characterizes some prior art. In addition,according to another aspect of the invention, an x-ray producing deviceis provided which can more readably be adapted for adjustment oralignment of the x-ray beam. For example, without the presence or needfor cooling fluids, an x-ray alignment or adjustment mechanism may beincorporated into x-ray device 1100, for example, for aligning x-raybeam 1130 with an x-ray optic, such as a capillary optic or crystaloptic, without requiring the alignment or adjustment mechanism to befluid tight. For example, one alignment mechanism that may be used withone aspect of the present invention is disclosed in copendingapplication No. 60/1336,584 filed Dec. 4, 2001 (attrny. docket0444.045P), the disclosure of which has been incorporated by referenceherein.

Improved Alignment and Stability Aspects of the Invention

As generally discussed above, the present invention provides in oneaspect an x-ray source assembly providing, for example, a focused x-raybeam or a collimated x-ray beam, and having a stable output over a rangeof operating conditions. This stable output is obtained via a controlsystem which controls positioning, in one aspect, of the anode sourcespot relative to an output structure of the assembly notwithstanding achange in one or more of the operating conditions. For example, theposition of the anode source spot can be maintained constant relative toan output structure notwithstanding change in the anode power level or achange in the ambient temperature about the x-ray source assembly.

The control system employs one or more actuators which can effectmovement of either the anode source spot or the output structure. Forexample, one actuator might comprise a temperature actuator whichprovides heating/cooling of the anode to effect adjustments in the anodesource spot location relative to the output structure. Another actuatormight comprise a mechanical actuator which would physically adjustposition of either the anode source spot or the output structure asneeded. Still another actuator might electrostatically or magneticallymove the electron beam. One or more sensors can be employed by thecontrol system to provide feedback on the anode source spot locationrelative to the output structure. The sensors may include temperaturesensors, such as a sensor to directly or indirectly measure the anodetemperature, as well as a housing temperature sensor and an ambienttemperature sensor. The sensors may also include a feedback mechanismfor obtaining the anode power level, or a direct or indirect measure ofthe optic output intensity.

In another aspect, an x-ray source assembly is disclosed which includesan x-ray tube having an anode for generating x-rays and an optic forcollecting x-rays generated by the anode. A control system is providedfor controlling x-ray output intensity from the optic. This controlsystem can maintain x-ray output intensity notwithstanding a change inone or more operating conditions of the x-ray source assembly. Forexample, the control system can adjust for a change in anode power leveland/or a change in ambient temperature. Various additional features ofthe invention are also described and claimed hereinbelow.

As used herein, the phrase “output structure” refers to a structurecomprising part of the x-ray source assembly or associated with thex-ray source assembly. By way of example, the structure could comprisean x-ray transmission window or an optic, such as a focusing orcollimating optic, which may or may not be secured to a housingsurrounding the x-ray tube within the assembly.

FIG. 12 illustrates in cross-section an elevational view of an x-raysource assembly 2100 in accordance with an aspect of the presentinvention. X-ray source assembly 2100 includes a x-ray source 2101comprising a vacuum tight x-ray tube 2105 (typically formed of glass orceramic) having a transmission window 2107. X-ray tube 2105 houses anelectron gun 2115 arranged opposite a high-voltage (HV) anode 2125. Whenvoltage is applied, electron gun 2115 emits electrons in the form of anelectron stream, i.e., an electron beam (e-beam) 2120, as is well knownin the art. HV anode 2125 acts as a target with a source spot upon whichthe electron stream impinges for producing x-ray radiation, i.e., x-rays2130.

By way of example, electron gun 2115 could be held at ground potential(zero volts), while HV anode 2125 is held at a high voltage potential,typically around 50 kv. As a result, e-beam 2120 emitted from electrongun 2115 at ground potential is electrically attracted to the surface ofHV anode 2125, thereby producing x-rays 2130 from a source spot on theanode where e-beam 2120 strikes the anode. X-rays 2130 are subsequentlydirected through transmission window 2107 of vacuum tight x-ray tube2105. Transmission window 2107 is typically formed of a material such asberyllium (Be) which permits substantially unimpeded transmission ofx-rays while still maintaining the vacuum within x-ray tube 2105.

A housing 2110 at least partially encloses x-ray tube 2105. Housing 2110can include an aperture 2112 aligned with transmission window 2107 ofx-ray tube 2105. By way of example, aperture 2112 could comprise an openaperture in housing 2110 or an enclosed aperture defining an air space.Upon transmission through transmission window 2107 and aperture 2112,x-rays 2130 are collected by an optic 2135. Optic 2135 is shown in thisexample centered about aperture 2112 in housing 2110. Optic 2135 couldbe affixed to an exterior surface of housing 2110, or could be partiallydisposed within housing 2110 to reside within aperture 2112 (e.g., toreside against transmission window 2107), or could be separatelysupported from housing 2110 but aligned to aperture 2112 in housing2110.

As noted, optic 2135 could comprise a focusing optic or a collimatingoptic, by way of example. In FIG. 12, optic 2135 is shown to be afocusing element, which is useful when x-ray source 2100 is utilized forapplications requiring a high intensity, low diameter spot 2145.Focusing optic 2135 collects x-ray radiation 2130 and focuses theradiation into converging x-rays 2140. A focusing optic could bebeneficial when x-ray source 2100 is to be employed in connection withan x-ray fluorescence system which requires a low power source. As analternative, optic 2135 could comprise a collimating optical element foruse in applications which require a parallel beam of x-ray radiationoutput from the optic (not shown). In the case of a collimating opticalelement, x-rays 2140 would be parallel rather than converging to spot2145 as shown in FIG. 12.

Optic 2135 could comprise any optical element capable of collecting ormanipulating x-rays, for example, for focusing or collimating. By way ofexample, optic 2135 could comprise a polycapillary bundle (such asavailable from X-ray Optical Systems, Inc. of Albany, N.Y.), a doublycurved optic or other optical element form, such as a filter, a pinholeor a slit. (A polycapillary optic is a bundle of thin, hollow tubes thattransmit photons via total reflection. Such an optic is described, forexample, in U.S. Pat. Nos. 5,175,755, 5,192,869, and 5,497,008. Doublycurved optics are described, for example, in U.S. Pat. Nos. 6,285,506and 6,317,483) Upon calibration of x-ray source assembly 2100, optic2135 remains stationary (in one embodiment) relative to x-ray source2101 until further calibration of x-ray source assembly 2100 isperformed.

The end of HV anode 2125 opposite the impingement surface protrudesthrough the body of x-ray tube 2105 and is mechanically and electricallyconnected to a base assembly 2150. Base assembly 2150 includes a firstconductor disc 2155 that is electrically isolated from a base plate 2165via a dielectric disc 2160. The resulting anode 2125 and base assembly2150 structure, referred to herein as the anode stack, is described indetail in the above-incorporated, co-filed patent application entitled“Method and Device For Cooling and Electrically Insulating AHigh-Voltage, Heat Generating Component”. Although described in greaterdetail therein, the structure and function of base assembly 2150 arebriefly discussed below.

Conductor disc 2155 and base plate 2165 are, for example, several-inchdiameter, disc-shaped plates formed of a highly electrically conductiveand highly thermally conductive material, such as copper. By way ofexample, conductor disc 2155 and base plate 2165 may have a thickness inthe range of 0.1 to 0.5 inches, with 0.25 inches being one specificexample. Base plate 2165 may further include constructional detail toaccommodate the overall structure of x-ray source 2101.

Dielectric disc 2160 is, for example, a 1.5-inch diameter, disc-shapedplate formed of a material that provides high dielectric strength athigh voltages, such as beryllium oxide ceramic or aluminum nitrideceramic. In addition, while not as thermally conductive as conductordisc 2155 or base plate 2165, these materials do exhibit relatively goodthermal conductivity. Dielectric disc 2150 may have a thickness in therange of 0.1 to 0.5 inches, with 0.25 inches being one specific example.

Conductor disc 2155 is mechanically and electrically connected to a highvoltage source (not shown) via an appropriate high voltage lead 2170. Asa result, the high voltage potential is supplied to conductor disc 2155and subsequently to HV anode 2125. Conversely, base plate 2165 is heldat ground potential. Dielectric disc 2160 provides electrical isolationbetween high-voltage conductor disc 2155 and the grounded base plate2165. One example of an assembly for connecting high voltage lead 2170to conductor disc 2155 is described in the above-incorporated, commonlyfiled patent application entitled “An Electrical Connector, A CableSleeve, and A Method For Fabricating A High Voltage ElectricalConnection For A High Voltage Device”.

The x-ray tube 2105, base assembly 2150, and HV lead 2170, are encasedin an encapsulant 2175. Encapsulant 2175 can comprise a rigid orsemi-rigid material with a sufficiently high dielectric strength toavoid voltage breakdown, such as silicone. Furthermore, encapsulant 2175need not be a good thermal conductor since the preferred thermal path isthrough base assembly 2150. As a specific example, encapsulant 2175could be formed by molding a silicon elastomer (such as Dow Sylgard® 184available from Dow Chemical), around the x-ray tube, base assembly andhigh voltage lead, thereby forming a structure which is void of airpockets which might provide an undesirable voltage breakdown path toground.

FIG. 13 graphically illustrates a source scan curve 2200 in which arepresentation of output intensity, e.g., spot 2145 (FIG. 12) intensity,is plotted with respect to displacement or misalignment between theanode source spot and the output optic. The spot intensity results fromscanning x-rays (2130) across the focal point of optic (2135). It isshown that a Gaussian plot results, in which a maximum intensity isachieved with proper alignment of x-rays 2130 (and thus the anode sourcespot) at the focal point of the optic.

As shown, the full width W1 at half maximum (FWHM) is equal toapproximately 200 microns. A FWHM of 200 microns indicates that thex-ray intensity at spot 2145 drops 50% as a result of displacement ofx-rays 2130 (and thus the anode source spot) a distance of 2100 micronsfrom the focal point of optic 2135. When properly calibrated, x-raysource assembly 2100 functions for a given power near the top of thesource scan curve of FIG. 13, where the slope is approximately equal tozero, such that minor perturbations in the displacement of x-rays 2130(e.g., 5 μm or less) with respect to optic 2135 result in a negligibleintensity drop. By way of example, the range of allowable perturbationsin the displacement of x-rays 2130 with respect to optic 2135 isrepresented by W2, indicating that a displacement less than five micronsbetween x-rays 2130 and the focal point of optics 2135 is acceptable.However, a difference in the thermal expansion of as much as 50 micronscan occur in HV anode 2125 and the elements of base assembly 2150 as theoperating power of the x-ray source varies from 0 to 50 W.

FIG. 14 depicts x-ray source 2100 as described above in connection withFIG. 12. In this example, however, heat generated by e-beam 2120impinging on HV anode 2125 has caused HV anode 2125, conductor disc2155, base plate 2165, and to a lesser extent, dielectric disc 2160, toexpand. As a result of this expansion, a divergent beam of x-rays 2310is generated that is displaced vertically with respect to x-rays 2130illustrated in FIG. 12. For example, if the electron gun 2115 isoperated at a power of 50 W, the focal point of x-rays 2310 may bedisplaced by as much as 50 microns from its position at 0 W. X-rays 2310are misaligned with optic 2135 and, as a result, the convergent beam ofx-rays 2315 produces a spot 2320 of markedly reduced intensity.

Due to the physical nature of collimating optics and focusing optics,such as doubly curved crystals and polycapillary bundles, precisepositioning of optic 2135 relative to the anode source spot is desirablefor optimum collimation or focusing of x-rays 2315. As a result, adisplacement of x-rays 2310 with respect to optic 2135 such as mayresult from thermal expansion of HV anode 2125 and base assembly 2150can result in a spot 2320 having significantly reduced intensity, asillustrated graphically in FIG. 13.

The anode source spot to an output structure offset can be measuredusing various approaches. For example, a temperature sensor 2400 couldbe employed at the base of the anode stack to measure changes in anodestack temperature, which as described further below can be correlated tothe anode source spot to optic offset during a calibration procedure.FIG. 16 shows an alternative temperature sensor implementation.

As shown in FIG. 16, base assembly 2150, again including conductor disc2155, dielectric disc 2160 and base plate 2165, is modified to include atemperature sensor 2400 recessed within and in good thermal contact withbase plate 2165. For illustrative purposes, FIG. 16 depicts waves whichrepresent heat transfer from the anode, to and through the baseassembly. These waves represent heat which is generated by theimpingement of e-beam 2120 upon HV anode 2125 as shown in FIG. 15.

Also depicted in FIG. 15 is an x-ray intensity measurement device 2410.In addition to, or as an alternative to, sensing temperature todetermine offset, x-ray output intensity of either x-ray source 2101 oroptic 2135 could be measured. By way of example, in a diffractionapplication, an ion chamber or a proportional counter could be used asan intensity measurement device 2410 in order to provide the neededfeedback for a position control system such as described herein. In adiffraction application, the energy of interest is typically only at onewavelength and thus a proportional counter disposed within the x-raypath only absorbs a small amount of the x-rays of interest. Thoseskilled in the art will recognize that other intensity measurementapproaches could be employed to directly or indirectly determine theintensity of x-rays output from the x-ray source assembly 2100. The goalof temperature sensing, x-ray intensity sensing, etc., is to providefeedback information on the alignment between the anode source spot andthe output structure. A control system and a control process aredescribed further below with reference to FIGS. 18-21.

The correlation between anode stack temperature and anode source spot tooutput structure alignment can be better understood with reference toFIGS. 17-17B.

In FIG. 17, an anode stack is shown comprising anode 2125 and baseassembly 2150. Assembly 2150 includes conductor disc 2155, dielectricdisc 2160 and base plate 2165, which in this example is shown withtemperature sensor 2400 embedded therein. The anode stack is positionedhorizontally in order to correlate with the distance axis (x-axis) onthe graph of FIG. 17A.

As shown in FIG. 17A, the anode stack has different temperature dropsacross the various components comprising the stack. Beginning at theright most end of anode 2125, for both a 50 W and 25 W example, there isshown a temperature drop which has a slope slightly steeper than thetemperature drop across, for example, conductor disc 2155. Although bothanode 2125 and disc 2155 are conductive, the larger cross-section fordisc 2155 means that there is less of a temperature drop from one mainsurface to the other. Also as shown in FIG. 17A, the change intemperature across the anode stack relates to the anode power level. Thechange in temperature (y-axis) refers to a changing temperature offsetof the anode stack above room temperature. Thus, at zero applied anodepower level the offset is assumed to be zero.

As a further enhancement, an x-ray source assembly in accordance with anaspect of the present invention could be adjusted to accommodate forchanges in room or ambient temperature. In order for the total thermalexpansion of the elements contributing to the expansion to be the sameat 50 W beam current as at 0 W beam current, then the 0 W basetemperature of plate 2165 (and hence the connected elements) can beraised to, for example, 40° C. This is shown in FIG. 17A by the dottedline.

FIG. 17B depicts an example of reference temperature less ambienttemperature of a component of the anode stack for various anode powerlevels between 0 and 50 Watts. More particularly, FIG. 17B depicts thereference temperature (derived and shown at 0 W in FIG. 17A) for varioustube operating powers. Further, by adding an additional temperatureoffset to this reference temperature, the same system can accommodatechanges in ambient temperature. For example, at 50 W and 20° C., a 0° C.reference delta temperature is obtained. If this reference deltatemperature is raised to 5° C., then additional heating is to besupplied to maintain this delta temperature at 20° C. However at 25° C.,no additional heating is required. In this way, an offset in thereference delta temperature is required at, for example, 20° C., whichallows for compensation at higher ambient temperatures.

FIG. 18 illustrates in cross-section an elevational view of oneembodiment of an x-ray source assembly, generally denoted 2700, inaccordance with a further aspect of the present invention. X-ray sourceassembly 2700 includes an x-ray source 2705 and an output optic 2135.Optic 2135 is aligned to x-ray transmission window 2107 of vacuum x-raytube 2105. X-ray tube 2105 again houses electron gun 2115 arrangedopposite to high voltage anode 2125. When voltage is applied, electrongun 2115 emits electrons in the form of an electron stream (i.e.,electron beam 2120 as described above). HV anode 2125 acts as a targetwith respect to a source spot upon which the electron stream impingesfor producing x-ray radiation 2130 for transmission through window 2107and collection by optic 2135. Electron gun 2115 and anode 2125 functionas described above in connection with the embodiments of FIGS. 12, 14 &15.

Anode 2125 is again physically and electrically connected to a baseassembly which includes a conductor plate 2155 that is electricallyisolated from a base plate 2165′ via a dielectric disc 2160. Theconstruction and function of the base assembly could be similar to thebase assemblies described above in connection with FIGS. 12, 14 & 15. Ahigh voltage lead 2170 connects to conductive plate 2155 to provide thedesired power level to anode 2125. The electron gun 2115, anode 2125,base assembly 2150 and high voltage lead 2170 are encased by encapsulant2175 all of which reside within a housing 2710. Housing 2710 includes anaperture 2712 aligned to x-ray transmission window 2107 of x-ray tube2105. In operation, x-ray radiation 2130 is collected by optic 2135, andin this example, focused 2740 to a spot 2745. As noted above, optic 2135may comprise any one of various types of optical elements, includingpolycapillary bundles and doubly curved crystals. Also, optic 2135 may,for example, comprise a focusing optic or a collimating optic dependingupon the application for the x-ray source assembly.

In accordance with an aspect of the present invention, a control systemis implemented within x-ray source assembly 2700. This control systemincludes, for example, a processor 2715, which is shown embedded withinhousing 2710, as well as one or more sensors and one or more actuators(such as sensor/actuator 2720 and actuator 2730), which would be coupledto processor 2715. This control system within x-ray source assembly 2700comprises functionality to compensate for, for example, thermalexpansion of HV anode 2125 and base assembly 2150 with changes in anodepower level in order to maintain an alignment of x-rays 2130 withrespect to optic 2135. This enables the x-ray source assembly 2700 tomaintain a spot size 2745 with stable intensity within a range of anodeoperating levels.

FIG. 19 depicts one embodiment of a control loop and FIG. 19A depictsone example of a control function, in accordance with an aspect of thepresent invention. As shown in FIG. 19, one or more sensors 2800 providefeedback on, for example, anode stack temperature and/or x-ray outputintensity, which is fed to a processor 2810 implementing the controlfunction. By way of example, FIG. 19A depicts a control function whereina temperature offset is determined between the value from a temperaturesensor (TS) and a reference temperature (R) in order that the currentposition (K), rate of change (d/dt) and accumulated history (S) can bedetermined. The results of this proportional integral derivativefunction are then summed to provide an output as a function of time(O(t)). This output is provided to one or more actuators 2820 whicheffect an automatic change in either the anode source spot location orthe location of an output structure (such as the optic), in order thatfor example, the anode source spot location is maintained relative tothe output structure or output intensity of the optic is held to adesired value. This monitoring and adjustment process could becontinuously repeated by the control system of the x-ray sourceassembly.

Returning to FIG. 18, sensor/actuator 2720 could include a temperatureactuator physically coupled to base plate 2165′. This temperatureactuator 2720 could comprise for example, any means for applying heatand/or applying cooling to base plate 2165′ in order to add/remove heatto/from the base plate. By way of example, the heating element mightcomprise a 10 Ohm power resistor such as model number MP850 availablefrom Caddock Electronics of Riverside, Calif., while an appropriatecooling element might comprise a forced air heat sink or a liquid basedheat sink. The temperature actuator can be utilized during operation ofthe x-ray source assembly to maintain the anode x-ray spot at an optimumorientation with respect to one or more output structures such as thex-ray collection optic. The application of heat or removal of heat fromthe base plate is accomplished so that a consistent average temperatureis maintained across the anode stack throughout operation of the x-raysource assembly notwithstanding change in one or more operatingconditions of the assembly, such as anode power level.

Specifically, in one embodiment, the thermal expansion of the baseassembly and HV anode are maintained within a tolerance that enables thegenerated x-rays to be consistently aligned with, for example, thecollection optic throughout the operating ranges of the x-ray sourceassembly. The addition of applied heat may occur, for example, when thex-ray source assembly shifts to a reduced operating power so that the HVanode and the base assembly elements do not undergo a reduction in sizedue to a reduced dissipation of heat therethrough, enabling an optimumalignment of x-rays and the collection optic to be maintained. In oneembodiment, the heating element could be included internal to the baseplate, while the cooling element might be thermally coupled to theexposed surface of the base plate.

Although described herein in connection with maintaining a consistentaverage temperature across the anode stack, those skilled in the artwill recognize that there are other mechanisms for maintaining thedesired alignment between the anode source spot and the outputstructure. For example, mechanical actuator(s) 2730 could be employed tophysically adjust the orientation and positioning of the collectionoptic relative to the anode source spot. These actuators could bemanually adjustable or automated so as to be responsive to a signalreceived from processor 2715. Other actuation control mechanisms willalso be apparent to those skilled in the art and are encompassed by theclaims presented herein. The goal of the control system is to maintain adesired orientation of the anode source spot relative to, e.g., thecollection optic input (i.e., focal point). Typically, this desiredorientation will comprise the optimum orientation which ensures thehighest intensity spot 2745.

FIG. 20 is a flowchart of one embodiment of processing which may beimplemented by processor 2715 of FIG. 18. FIG. 20 represents a loopwhich is periodically repeated by the processor during operation of thex-ray source assembly to, for example, apply or remove heat from thebase assembly in response to a change in one or more operatingconditions, such as the power level applied to the anode, and therebymaintain a consistent average temperature across the anode stack andthus enable the emitted x-rays to be optimally aligned with respect tothe input of the collection optic.

As shown in FIG. 20, processing begins by reading the anode power level2900. In one embodiment, the anode power level can be determined fromtwo analog inputs whose signals range, for example, between 0 and 10 V.One input communicates the voltage at which the power supply supplyingpower to e-gun 2115 (FIG. 18) is operating, while a second inputcommunicates the amperage being drawn by the power supply. From thesetwo inputs, the power at which e-gun 2115 is operating may bedetermined, which is also the power level of the anode.

Processing next reads the temperature of the anode stack as well as thesource housing 2910. As noted above, the temperature of the anode stackcan be obtained from the base plate of the base assembly using atemperature sensor, with the resultant signal fed back to the processorembedded within the assembly. The housing temperature also couldcomprise a temperature sensor, which in one embodiment, would bethermally coupled to a surface of the housing in order to measureexpansion or contraction of the enclosure. The desirability of measuringhousing temperature assumes that the optic or other output structurebeing monitored is mechanically coupled to the housing.

Next, processing determines a reference temperature for the read powerlevel 2920. The reference temperature would be a desirable predeterminedtemperature for the anode stack at the measured anode power level.Reference temperatures could be determined during a calibrationprocedure for the x-ray source assembly, and may either be unique to aparticular assembly or generic to a plurality of identicallymanufactured x-ray source assemblies. FIG. 21 depicts one embodiment ofa table which could be employed in order to look up the referencetemperature for a read power level. As shown, the table of FIG. 21 alsoemploys the housing temperature as another operating condition to beconsidered in determining the desired reference temperature for theanode stack. Thus, depending upon the housing temperature for the x-raysource assembly and the anode power level, a desired referencetemperature for the anode stack is obtained.

The reference temperature and the read temperatures are fed to aposition, rate and accumulated history control algorithm such asdescribed above in connection with FIG. 19. The algorithm is employed tocalculate the outputs to the one or more actuators 2930. One of ordinaryskill in the art can readily implement a proportion integral derivativealgorithm to accomplish this function. Once the output is obtained, theoutput is provided to the actuator(s) in order to, for example, maintainthe anode source spot location relative to the optic input 2940.

As one specific example, the processor could output a signal whichcomprises a pulse width modulated signal that enables the cooling fan tooperate at a range of rotational speeds, and thereby remove heat at anappropriate rate from the base plate of the anode stack. The duty cycleis such a pulse width modulated output can be determined by theoperating power of the anode. A second output could enable variation inthe power supplied to the heating element, and thereby variations in theamount of heat added to the base plate of the anode stack. In oneembodiment, the processor, after performing the proportional integraldifferential (PID) algorithm, could utilize a formula or a look-up tableto determine the temperature that the base plate of the anode stackshould be maintained at (i.e., reference temperature) for a particularpower level at which the anode is currently operating.

As an alternative to the above-described feedback based algorithm, theprocessor could implement (by way of example) a model or predictivebased algorithm. As an example of a predictive based algorithm, thesource and optic could be intentionally misaligned in order to identifyan accurate starting position on a known source scan curve. For example,the source and optic alignment could be misplaced to a high slopeposition on the source scan curve, thereby allowing the displacement tobe accurately measured or inferred. Thereafter, using the determineddisplacement, an adjustment can be made using the known source scancurve to return to the peak of the curve.

While the invention has been particularly shown and described withreference to preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and details may be madeto the invention without departing from the spirit and scope of theinvention described in the following claims.

1. A wavelength dispersive apparatus for analyzing a fluid using x-rays,comprising: means for exposing the fluid to focused x-rays to cause atleast one component of the fluid to x-ray fluoresce, including: afocusing optic for focusing the x-rays on the fluid, and at least onex-ray exposure chamber aperture less than about 10 mm in diameter; meansfor analyzing monochromatic x-ray fluorescence to determine at least onecharacteristic of the fluid, including: at least one x-ray detectorhaving an active area operating at a temperature greater than about 0degrees centigrade and substantially uncooled; and a focusing optic tocollect x-ray fluorescence from the fluid, and focus said x-rayfluorescence on the detector.
 2. The apparatus of claim 1, wherein theat least one characteristic of the fluid comprises a concentration of atleast one component in the fluid.
 3. The apparatus of claim 2, whereinthe fluid is fuel, and the at least one characteristic is theconcentration of sulfur in the fuel.
 4. The apparatus of claim 1,wherein the detector comprises at least one semiconductor-type x-raydetector.
 5. The apparatus of claim 4, wherein the detector comprises atleast one PIN-diode-semiconductor-type x-ray detector.
 6. The apparatusof claim 4, wherein the semiconductor-type x-ray detector comprises adetector active area having an area less than about 10 squaremillimeters.
 7. The apparatus of claim 6, wherein the semiconductor-typex-ray detector comprises a detector active area having an area less thanabout 6 square millimeters.
 8. The apparatus of claim 1, wherein themeans for exposing the fluid to x-rays is enclosed in a chamber heldunder vacuum.
 9. The apparatus of claim 1, wherein the focusing optic isa focusing monochromator.
 10. The apparatus of claim 1, wherein thedetector has no protective window.
 11. The apparatus of claim 1, whereinthe x-ray exposure aperture is less than about 5 mm in diameter.
 12. Theapparatus of claim 1, wherein the fluid comprises a continuous,pressurized fluid stream, the apparatus further comprising: means fordelivering the continuous fluid stream to the means for analyzing. 13.The apparatus of claim 1, further comprising: an x-ray source includingan x-ray tube for generating the x-rays; and a thermally-conductive,dielectric material thermally coupled to the x-ray tube for removingheat generated by the x-ray tube.
 14. The apparatus of claim 1, furthercomprising: an x-ray tube having an anode for generating x-rays; anoptic for collecting x-rays generated by the anode; and a control systemfor controlling x-ray output intensity of the optic, wherein the controlsystem can maintain x-ray output intensity notwithstanding a change inat least one operating condition of the apparatus.
 15. The apparatus ofclaim 14, wherein the control system further includes a sensor formonitoring x-ray output intensity of the optic and a controller forcontrolling position of at least one of the anode and the optic usingmonitored x-ray output intensity.
 16. The apparatus of claim 1, whereinat least one of the focusing optics comprises a polycapillary focusingoptic.
 17. The apparatus of claim 1, wherein at least one of thefocusing optics comprises a curved crystal monochromating optic.
 18. Theapparatus of claim 17, wherein both focusing optics comprise doublycurved crystal monochromating optics.